diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -2218,6 +2218,15 @@ def displaygraph(ui, repo, dag, displaye
                  filematcher=None):
     formatnode = _graphnodeformatter(ui, displayer)
     state = graphmod.asciistate()
+    styles = state['styles']
+    edgetypes = {
+        'parent': graphmod.PARENT,
+        'grandparent': graphmod.GRANDPARENT,
+        'missing': graphmod.MISSINGPARENT
+    }
+    for name, key in edgetypes.items():
+        # experimental config: ui.graphstyle.*
+        styles[key] = ui.config('ui', 'graphstyle.%s' % name, styles[key])
     for rev, type, ctx, parents in dag:
         char = formatnode(repo, ctx)
         copies = None
diff --git a/mercurial/graphmod.py b/mercurial/graphmod.py
--- a/mercurial/graphmod.py
+++ b/mercurial/graphmod.py
@@ -31,6 +31,7 @@ CHANGESET = 'C'
 PARENT = 'P'
 GRANDPARENT = 'G'
 MISSINGPARENT = 'M'
+EDGES = {PARENT: '|', GRANDPARENT: '|', MISSINGPARENT: '|'}
 
 def groupbranchiter(revs, parentsfunc, firstbranch=()):
     """Yield revisions from heads to roots one (topo) branch at a time.
@@ -390,11 +391,13 @@ def asciiedges(type, char, lines, state,
             knownparents.append(parent)
         else:
             newparents.append(parent)
+            state['edges'][parent] = state['styles'].get(ptype, '|')
 
     ncols = len(seen)
     nextseen = seen[:]
     nextseen[nodeidx:nodeidx + 1] = newparents
-    edges = [(nodeidx, nextseen.index(p)) for p in knownparents if p != nullrev]
+    edges = [(nodeidx, nextseen.index(p))
+             for p in knownparents if p != nullrev]
 
     while len(newparents) > 2:
         # ascii() only knows how to add or remove a single column between two
@@ -418,6 +421,8 @@ def asciiedges(type, char, lines, state,
         edges.append((nodeidx, nodeidx + 1))
     nmorecols = len(nextseen) - ncols
     seen[:] = nextseen
+    # remove current node from edge characters, no longer needed
+    state['edges'].pop(rev, None)
     yield (type, char, lines, (nodeidx, edges, ncols, nmorecols))
 
 def _fixlongrightedges(edges):
@@ -426,27 +431,28 @@ def _fixlongrightedges(edges):
             edges[i] = (start, end + 1)
 
 def _getnodelineedgestail(
-        node_index, p_node_index, n_columns, n_columns_diff, p_diff, fix_tail):
-    if fix_tail and n_columns_diff == p_diff and n_columns_diff != 0:
+        echars, idx, pidx, ncols, coldiff, pdiff, fix_tail):
+    if fix_tail and coldiff == pdiff and coldiff != 0:
         # Still going in the same non-vertical direction.
-        if n_columns_diff == -1:
-            start = max(node_index + 1, p_node_index)
-            tail = ["|", " "] * (start - node_index - 1)
-            tail.extend(["/", " "] * (n_columns - start))
+        if coldiff == -1:
+            start = max(idx + 1, pidx)
+            tail = echars[idx * 2:(start - 1) * 2]
+            tail.extend(["/", " "] * (ncols - start))
             return tail
         else:
-            return ["\\", " "] * (n_columns - node_index - 1)
+            return ["\\", " "] * (ncols - idx - 1)
     else:
-        return ["|", " "] * (n_columns - node_index - 1)
+        remainder = (ncols - idx - 1)
+        return echars[-(remainder * 2):] if remainder > 0 else []
 
-def _drawedges(edges, nodeline, interline):
+def _drawedges(echars, edges, nodeline, interline):
     for (start, end) in edges:
         if start == end + 1:
             interline[2 * end + 1] = "/"
         elif start == end - 1:
             interline[2 * start + 1] = "\\"
         elif start == end:
-            interline[2 * start] = "|"
+            interline[2 * start] = echars[2 * start]
         else:
             if 2 * end >= len(nodeline):
                 continue
@@ -457,26 +463,35 @@ def _drawedges(edges, nodeline, interlin
                 if nodeline[i] != "+":
                     nodeline[i] = "-"
 
-def _getpaddingline(ni, n_columns, edges):
-    line = []
-    line.extend(["|", " "] * ni)
-    if (ni, ni - 1) in edges or (ni, ni) in edges:
-        # (ni, ni - 1)      (ni, ni)
+def _getpaddingline(echars, idx, ncols, edges):
+    # all edges up to the current node
+    line = echars[:idx * 2]
+    # an edge for the current node, if there is one
+    if (idx, idx - 1) in edges or (idx, idx) in edges:
+        # (idx, idx - 1)      (idx, idx)
         # | | | |           | | | |
         # +---o |           | o---+
-        # | | c |           | c | |
+        # | | X |           | X | |
         # | |/ /            | |/ /
         # | | |             | | |
-        c = "|"
+        line.extend(echars[idx * 2:(idx + 1) * 2])
     else:
-        c = " "
-    line.extend([c, " "])
-    line.extend(["|", " "] * (n_columns - ni - 1))
+        line.extend('  ')
+    # all edges to the right of the current node
+    remainder = ncols - idx - 1
+    if remainder > 0:
+        line.extend(echars[-(remainder * 2):])
     return line
 
 def asciistate():
     """returns the initial value for the "state" argument to ascii()"""
-    return {'seen': [], 'lastcoldiff': 0, 'lastindex': 0}
+    return {
+        'seen': [],
+        'edges': {},
+        'lastcoldiff': 0,
+        'lastindex': 0,
+        'styles': EDGES.copy(),
+    }
 
 def ascii(ui, state, type, char, text, coldata):
     """prints an ASCII graph of the DAG
@@ -498,9 +513,15 @@ def ascii(ui, state, type, char, text, c
         in the current revision. That is: -1 means one column removed;
         0 means no columns added or removed; 1 means one column added.
     """
-
     idx, edges, ncols, coldiff = coldata
     assert -2 < coldiff < 2
+
+    edgemap, seen = state['edges'], state['seen']
+    # Be tolerant of history issues; make sure we have at least ncols + coldiff
+    # elements to work with. See test-glog.t for broken history test cases.
+    echars = [c for p in seen for c in (edgemap.get(p, '|'), ' ')]
+    echars.extend(('|', ' ') * max(ncols + coldiff - len(seen), 0))
+
     if coldiff == -1:
         # Transform
         #
@@ -530,35 +551,33 @@ def ascii(ui, state, type, char, text, c
     fix_nodeline_tail = len(text) <= 2 and not add_padding_line
 
     # nodeline is the line containing the node character (typically o)
-    nodeline = ["|", " "] * idx
+    nodeline = echars[:idx * 2]
     nodeline.extend([char, " "])
 
     nodeline.extend(
-        _getnodelineedgestail(idx, state['lastindex'], ncols, coldiff,
-                              state['lastcoldiff'], fix_nodeline_tail))
+        _getnodelineedgestail(
+            echars, idx, state['lastindex'], ncols, coldiff,
+            state['lastcoldiff'], fix_nodeline_tail))
 
     # shift_interline is the line containing the non-vertical
     # edges between this entry and the next
-    shift_interline = ["|", " "] * idx
+    shift_interline = echars[:idx * 2]
+    shift_interline.extend(' ' * (2 + coldiff))
+    count = ncols - idx - 1
     if coldiff == -1:
-        n_spaces = 1
-        edge_ch = "/"
+        shift_interline.extend('/ ' * count)
     elif coldiff == 0:
-        n_spaces = 2
-        edge_ch = "|"
+        shift_interline.extend(echars[(idx + 1) * 2:ncols * 2])
     else:
-        n_spaces = 3
-        edge_ch = "\\"
-    shift_interline.extend(n_spaces * [" "])
-    shift_interline.extend([edge_ch, " "] * (ncols - idx - 1))
+        shift_interline.extend(r'\ ' * count)
 
     # draw edges from the current node to its parents
-    _drawedges(edges, nodeline, shift_interline)
+    _drawedges(echars, edges, nodeline, shift_interline)
 
     # lines is the list of all graph lines to print
     lines = [nodeline]
     if add_padding_line:
-        lines.append(_getpaddingline(idx, ncols, edges))
+        lines.append(_getpaddingline(echars, idx, ncols, edges))
     lines.append(shift_interline)
 
     # make sure that there are as many graph lines as there are
@@ -566,7 +585,7 @@ def ascii(ui, state, type, char, text, c
     while len(text) < len(lines):
         text.append("")
     if len(lines) < len(text):
-        extra_interline = ["|", " "] * (ncols + coldiff)
+        extra_interline = echars[:(ncols + coldiff) * 2]
         while len(lines) < len(text):
             lines.append(extra_interline)
 
diff --git a/tests/test-glog.t b/tests/test-glog.t
--- a/tests/test-glog.t
+++ b/tests/test-glog.t
@@ -2415,3 +2415,214 @@ label() should just work in node templat
   |
 
   $ cd ..
+
+change graph edge styling
+
+  $ cd repo
+  $ cat << EOF >> $HGRCPATH
+  > [ui]
+  > graphstyle.parent = |
+  > graphstyle.grandparent = :
+  > graphstyle.missing = .
+  > EOF
+  $ hg log -G -r 'file("a")' -m
+  @  changeset:   36:08a19a744424
+  :  branch:      branch
+  :  tag:         tip
+  :  parent:      35:9159c3644c5e
+  :  parent:      35:9159c3644c5e
+  :  user:        test
+  :  date:        Thu Jan 01 00:00:36 1970 +0000
+  :  summary:     (36) buggy merge: identical parents
+  :
+  o    changeset:   32:d06dffa21a31
+  |\   parent:      27:886ed638191b
+  | :  parent:      31:621d83e11f67
+  | :  user:        test
+  | :  date:        Thu Jan 01 00:00:32 1970 +0000
+  | :  summary:     (32) expand
+  | :
+  o :  changeset:   31:621d83e11f67
+  |\:  parent:      21:d42a756af44d
+  | :  parent:      30:6e11cd4b648f
+  | :  user:        test
+  | :  date:        Thu Jan 01 00:00:31 1970 +0000
+  | :  summary:     (31) expand
+  | :
+  o :    changeset:   30:6e11cd4b648f
+  |\ \   parent:      28:44ecd0b9ae99
+  | . :  parent:      29:cd9bb2be7593
+  | . :  user:        test
+  | . :  date:        Thu Jan 01 00:00:30 1970 +0000
+  | . :  summary:     (30) expand
+  | . :
+  o . :    changeset:   28:44ecd0b9ae99
+  |\ \ \   parent:      1:6db2ef61d156
+  | . . :  parent:      26:7f25b6c2f0b9
+  | . . :  user:        test
+  | . . :  date:        Thu Jan 01 00:00:28 1970 +0000
+  | . . :  summary:     (28) merge zero known
+  | . . :
+  o . . :    changeset:   26:7f25b6c2f0b9
+  |\ \ \ \   parent:      18:1aa84d96232a
+  | | . . :  parent:      25:91da8ed57247
+  | | . . :  user:        test
+  | | . . :  date:        Thu Jan 01 00:00:26 1970 +0000
+  | | . . :  summary:     (26) merge one known; far right
+  | | . . :
+  | o-----+  changeset:   25:91da8ed57247
+  | | . . :  parent:      21:d42a756af44d
+  | | . . :  parent:      24:a9c19a3d96b7
+  | | . . :  user:        test
+  | | . . :  date:        Thu Jan 01 00:00:25 1970 +0000
+  | | . . :  summary:     (25) merge one known; far left
+  | | . . :
+  | o . . :    changeset:   24:a9c19a3d96b7
+  | |\ \ \ \   parent:      0:e6eb3150255d
+  | | . . . :  parent:      23:a01cddf0766d
+  | | . . . :  user:        test
+  | | . . . :  date:        Thu Jan 01 00:00:24 1970 +0000
+  | | . . . :  summary:     (24) merge one known; immediate right
+  | | . . . :
+  | o---+ . :  changeset:   23:a01cddf0766d
+  | | . . . :  parent:      1:6db2ef61d156
+  | | . . . :  parent:      22:e0d9cccacb5d
+  | | . . . :  user:        test
+  | | . . . :  date:        Thu Jan 01 00:00:23 1970 +0000
+  | | . . . :  summary:     (23) merge one known; immediate left
+  | | . . . :
+  | o-------+  changeset:   22:e0d9cccacb5d
+  | . . . . :  parent:      18:1aa84d96232a
+  |/ / / / /   parent:      21:d42a756af44d
+  | . . . :    user:        test
+  | . . . :    date:        Thu Jan 01 00:00:22 1970 +0000
+  | . . . :    summary:     (22) merge two known; one far left, one far right
+  | . . . :
+  | . . . o    changeset:   21:d42a756af44d
+  | . . . |\   parent:      19:31ddc2c1573b
+  | . . . | |  parent:      20:d30ed6450e32
+  | . . . | |  user:        test
+  | . . . | |  date:        Thu Jan 01 00:00:21 1970 +0000
+  | . . . | |  summary:     (21) expand
+  | . . . | |
+  +-+-------o  changeset:   20:d30ed6450e32
+  | . . . |    parent:      0:e6eb3150255d
+  | . . . |    parent:      18:1aa84d96232a
+  | . . . |    user:        test
+  | . . . |    date:        Thu Jan 01 00:00:20 1970 +0000
+  | . . . |    summary:     (20) merge two known; two far right
+  | . . . |
+  | . . . o    changeset:   19:31ddc2c1573b
+  | . . . |\   parent:      15:1dda3f72782d
+  | . . . | |  parent:      17:44765d7c06e0
+  | . . . | |  user:        test
+  | . . . | |  date:        Thu Jan 01 00:00:19 1970 +0000
+  | . . . | |  summary:     (19) expand
+  | . . . | |
+  o---+---+ |  changeset:   18:1aa84d96232a
+    . . . | |  parent:      1:6db2ef61d156
+   / / / / /   parent:      15:1dda3f72782d
+  . . . | |    user:        test
+  . . . | |    date:        Thu Jan 01 00:00:18 1970 +0000
+  . . . | |    summary:     (18) merge two known; two far left
+  . . . | |
+  . . . | o    changeset:   17:44765d7c06e0
+  . . . | |\   parent:      12:86b91144a6e9
+  . . . | | |  parent:      16:3677d192927d
+  . . . | | |  user:        test
+  . . . | | |  date:        Thu Jan 01 00:00:17 1970 +0000
+  . . . | | |  summary:     (17) expand
+  . . . | | |
+  +-+-------o  changeset:   16:3677d192927d
+  . . . | |    parent:      0:e6eb3150255d
+  . . . | |    parent:      1:6db2ef61d156
+  . . . | |    user:        test
+  . . . | |    date:        Thu Jan 01 00:00:16 1970 +0000
+  . . . | |    summary:     (16) merge two known; one immediate right, one near right
+  . . . | |
+  . . . o |    changeset:   15:1dda3f72782d
+  . . . |\ \   parent:      13:22d8966a97e3
+  . . . | | |  parent:      14:8eac370358ef
+  . . . | | |  user:        test
+  . . . | | |  date:        Thu Jan 01 00:00:15 1970 +0000
+  . . . | | |  summary:     (15) expand
+  . . . | | |
+  +-------o |  changeset:   14:8eac370358ef
+  . . . | |/   parent:      0:e6eb3150255d
+  . . . | |    parent:      12:86b91144a6e9
+  . . . | |    user:        test
+  . . . | |    date:        Thu Jan 01 00:00:14 1970 +0000
+  . . . | |    summary:     (14) merge two known; one immediate right, one far right
+  . . . | |
+  . . . o |    changeset:   13:22d8966a97e3
+  . . . |\ \   parent:      9:7010c0af0a35
+  . . . | | |  parent:      11:832d76e6bdf2
+  . . . | | |  user:        test
+  . . . | | |  date:        Thu Jan 01 00:00:13 1970 +0000
+  . . . | | |  summary:     (13) expand
+  . . . | | |
+  . +---+---o  changeset:   12:86b91144a6e9
+  . . . | |    parent:      1:6db2ef61d156
+  . . . | |    parent:      9:7010c0af0a35
+  . . . | |    user:        test
+  . . . | |    date:        Thu Jan 01 00:00:12 1970 +0000
+  . . . | |    summary:     (12) merge two known; one immediate right, one far left
+  . . . | |
+  . . . | o    changeset:   11:832d76e6bdf2
+  . . . | |\   parent:      6:b105a072e251
+  . . . | | |  parent:      10:74c64d036d72
+  . . . | | |  user:        test
+  . . . | | |  date:        Thu Jan 01 00:00:11 1970 +0000
+  . . . | | |  summary:     (11) expand
+  . . . | | |
+  +---------o  changeset:   10:74c64d036d72
+  . . . | |/   parent:      0:e6eb3150255d
+  . . . | |    parent:      6:b105a072e251
+  . . . | |    user:        test
+  . . . | |    date:        Thu Jan 01 00:00:10 1970 +0000
+  . . . | |    summary:     (10) merge two known; one immediate left, one near right
+  . . . | |
+  . . . o |    changeset:   9:7010c0af0a35
+  . . . |\ \   parent:      7:b632bb1b1224
+  . . . | | |  parent:      8:7a0b11f71937
+  . . . | | |  user:        test
+  . . . | | |  date:        Thu Jan 01 00:00:09 1970 +0000
+  . . . | | |  summary:     (9) expand
+  . . . | | |
+  +-------o |  changeset:   8:7a0b11f71937
+  . . . |/ /   parent:      0:e6eb3150255d
+  . . . | |    parent:      7:b632bb1b1224
+  . . . | |    user:        test
+  . . . | |    date:        Thu Jan 01 00:00:08 1970 +0000
+  . . . | |    summary:     (8) merge two known; one immediate left, one far right
+  . . . | |
+  . . . o |    changeset:   7:b632bb1b1224
+  . . . |\ \   parent:      2:3d9a33b8d1e1
+  . . . | . |  parent:      5:4409d547b708
+  . . . | . |  user:        test
+  . . . | . |  date:        Thu Jan 01 00:00:07 1970 +0000
+  . . . | . |  summary:     (7) expand
+  . . . | . |
+  . . . +---o  changeset:   6:b105a072e251
+  . . . | ./   parent:      2:3d9a33b8d1e1
+  . . . | .    parent:      5:4409d547b708
+  . . . | .    user:        test
+  . . . | .    date:        Thu Jan 01 00:00:06 1970 +0000
+  . . . | .    summary:     (6) merge two known; one immediate left, one far left
+  . . . | .
+  . . . o .    changeset:   5:4409d547b708
+  . . . |\ \   parent:      3:27eef8ed80b4
+  . . . | . .  parent:      4:26a8bac39d9f
+  . . . | . .  user:        test
+  . . . | . .  date:        Thu Jan 01 00:00:05 1970 +0000
+  . . . | . .  summary:     (5) expand
+  . . . | . .
+  . +---o . .  changeset:   4:26a8bac39d9f
+  . . . ./ /   parent:      1:6db2ef61d156
+  . . . . .    parent:      3:27eef8ed80b4
+  . . . . .    user:        test
+  . . . . .    date:        Thu Jan 01 00:00:04 1970 +0000
+  . . . . .    summary:     (4) merge two known; one immediate left, one immediate right
+  . . . . .
+
+  $ cd ..