diff --git a/hgext/extdiff.py b/hgext/extdiff.py
--- a/hgext/extdiff.py
+++ b/hgext/extdiff.py
@@ -147,7 +147,12 @@ def dodiff(ui, repo, cmdline, pats, opts
 
     matcher = scmutil.match(repo[node2], pats, opts)
 
-    if True:
+    if opts.get('patch'):
+        if subrepos:
+            raise util.Abort(_('--patch cannot be used with --subrepos'))
+        if node2 is None:
+            raise util.Abort(_('--patch requires two revisions'))
+    else:
         mod_a, add_a, rem_a = map(set, repo.status(node1a, node2, matcher,
                                                    listsubrepos=subrepos)[:3])
         if do3way:
@@ -163,7 +168,7 @@ def dodiff(ui, repo, cmdline, pats, opts
 
     tmproot = tempfile.mkdtemp(prefix='extdiff.')
     try:
-        if True:
+        if not opts.get('patch'):
             # Always make a copy of node1a (and node1b, if applicable)
             dir1a_files = mod_a | rem_a | ((mod_b | add_b) - add_a)
             dir1a = snapshot(ui, repo, dir1a_files, node1a, tmproot,
@@ -217,6 +222,18 @@ def dodiff(ui, repo, cmdline, pats, opts
                         dir1b = os.devnull
                 dir2 = os.path.join(dir2root, dir2, common_file)
                 label2 = common_file + rev2
+        else:
+            # XXX: export doesn't support -I/-X like extdiff does
+            template = 'hg-%h.patch'
+            cmdutil.export(repo, [repo[node1a].rev(), repo[node2].rev()],
+                           template=repo.vfs.reljoin(tmproot, template))
+            label1a = cmdutil.makefilename(repo, template, node1a)
+            label2 = cmdutil.makefilename(repo, template, node2)
+            dir1a = repo.vfs.reljoin(tmproot, label1a)
+            dir2 = repo.vfs.reljoin(tmproot, label2)
+            dir1b = None
+            label1b = None
+            fns_and_mtime = []
 
         # Function to quote file/dir names in the argument string.
         # When not operating in 3-way mode, an empty string is
@@ -260,6 +277,7 @@ def dodiff(ui, repo, cmdline, pats, opts
      _('pass option to comparison program'), _('OPT')),
     ('r', 'rev', [], _('revision'), _('REV')),
     ('c', 'change', '', _('change made by revision'), _('REV')),
+    ('', 'patch', None, _('compare patches for two revisions'))
     ] + commands.walkopts + commands.subrepoopts,
     _('hg extdiff [OPT]... [FILE]...'),
     inferrepo=True)
diff --git a/tests/test-extdiff.t b/tests/test-extdiff.t
--- a/tests/test-extdiff.t
+++ b/tests/test-extdiff.t
@@ -46,6 +46,7 @@ Should diff cloned directories:
    -o --option OPT [+]      pass option to comparison program
    -r --rev REV [+]         revision
    -c --change REV          change made by revision
+      --patch               compare patches for two revisions
    -I --include PATTERN [+] include names matching the given patterns
    -X --exclude PATTERN [+] exclude names matching the given patterns
    -S --subrepos            recurse into subrepositories
diff --git a/tests/test-extension.t b/tests/test-extension.t
--- a/tests/test-extension.t
+++ b/tests/test-extension.t
@@ -390,6 +390,7 @@ Extension module help vs command help:
    -o --option OPT [+]      pass option to comparison program
    -r --rev REV [+]         revision
    -c --change REV          change made by revision
+      --patch               compare patches for two revisions
    -I --include PATTERN [+] include names matching the given patterns
    -X --exclude PATTERN [+] exclude names matching the given patterns
    -S --subrepos            recurse into subrepositories
diff --git a/tests/test-graft.t b/tests/test-graft.t
--- a/tests/test-graft.t
+++ b/tests/test-graft.t
@@ -332,6 +332,38 @@ Disallow grafting an already grafted cse
   skipping already grafted revision 7:ef0ef43d49e7 (was grafted from 2:5c095ad7e90f)
   [255]
 
+  $ hg extdiff --config extensions.extdiff= --patch -r 2 -r 13
+  --- */hg-5c095ad7e90f.patch	* +0000 (glob)
+  +++ */hg-7a4785234d87.patch	* +0000 (glob)
+  @@ -1,18 +1,18 @@
+   # HG changeset patch
+  -# User test
+  +# User foo
+   # Date 0 0
+   #      Thu Jan 01 00:00:00 1970 +0000
+  -# Node ID 5c095ad7e90f871700f02dd1fa5012cb4498a2d4
+  -# Parent  5d205f8b35b66bc36375c9534ffd3237730e8f04
+  +# Node ID 7a4785234d87ec1aa420ed6b11afe40fa73e12a9
+  +# Parent  b592ea63bb0c19a6c5c44685ee29a2284f9f1b8f
+   2
+   
+  -diff -r 5d205f8b35b6 -r 5c095ad7e90f a
+  +diff -r b592ea63bb0c -r 7a4785234d87 a
+   --- a/a	Thu Jan 01 00:00:00 1970 +0000
+   +++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
+   @@ -1,1 +0,0 @@
+  --b
+  -diff -r 5d205f8b35b6 -r 5c095ad7e90f b
+  +-a
+  +diff -r b592ea63bb0c -r 7a4785234d87 b
+   --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+   +++ b/b	Thu Jan 01 00:00:00 1970 +0000
+   @@ -0,0 +1,1 @@
+  -+b
+  ++a
+  [1]
+
+
 Disallow grafting already grafted csets with the same origin onto each other
   $ hg up -q 13
   $ hg graft 2