diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -1351,6 +1351,11 @@ def debugdate(ui, date, range=None, **op
         m = util.matchdate(range)
         ui.write("match: %s\n" % m(d[0]))
 
+def debugignore(ui, repo, *values, **opts):
+    """display the combined ignore pattern"""
+    ignore = repo.dirstate._ignore
+    ui.write("%s\n" % ignore.includepat)
+
 def debugindex(ui, repo, file_, **opts):
     """dump the contents of an index file"""
     r = None
@@ -4347,6 +4352,7 @@ table = {
          _('[-e] DATE [RANGE]')),
     "debugdata": (debugdata, [], _('FILE REV')),
     "debugfsinfo": (debugfsinfo, [], _('[PATH]')),
+    "debugignore": (debugignore, [], ''),
     "debugindex": (debugindex,
                    [('f', 'format', 0, _('revlog format'), _('FORMAT'))],
                    _('FILE')),
diff --git a/mercurial/match.py b/mercurial/match.py
--- a/mercurial/match.py
+++ b/mercurial/match.py
@@ -39,11 +39,11 @@ class match(object):
         self._anypats = bool(include or exclude)
 
         if include:
-            im = _buildmatch(_normalize(include, 'glob', root, cwd, auditor),
-                             '(?:/|$)')
+            pats = _normalize(include, 'glob', root, cwd, auditor)
+            self.includepat, im = _buildmatch(pats, '(?:/|$)')
         if exclude:
-            em = _buildmatch(_normalize(exclude, 'glob', root, cwd, auditor),
-                             '(?:/|$)')
+            pats = _normalize(exclude, 'glob', root, cwd, auditor)
+            self.excludepat, em = _buildmatch(pats, '(?:/|$)')
         if exact:
             self._files = patterns
             pm = self.exact
@@ -51,7 +51,7 @@ class match(object):
             pats = _normalize(patterns, default, root, cwd, auditor)
             self._files = _roots(pats)
             self._anypats = self._anypats or _anypats(pats)
-            pm = _buildmatch(pats, '$')
+            self.patternspat, pm = _buildmatch(pats, '$')
 
         if patterns or exact:
             if include:
@@ -246,7 +246,7 @@ def _buildmatch(pats, tail):
         pat = '(?:%s)' % '|'.join([_regex(k, p, tail) for (k, p) in pats])
         if len(pat) > 20000:
             raise OverflowError()
-        return re.compile(pat).match
+        return pat, re.compile(pat).match
     except OverflowError:
         # We're using a Python with a tiny regex engine and we
         # made it explode, so we'll divide the pattern list in two
@@ -254,8 +254,9 @@ def _buildmatch(pats, tail):
         l = len(pats)
         if l < 2:
             raise
-        a, b = _buildmatch(pats[:l//2], tail), _buildmatch(pats[l//2:], tail)
-        return lambda s: a(s) or b(s)
+        pata, a = _buildmatch(pats[:l//2], tail),
+        patb, b = _buildmatch(pats[l//2:], tail)
+        return pat, lambda s: a(s) or b(s)
     except re.error:
         for k, p in pats:
             try:
diff --git a/tests/test-debugcomplete.t b/tests/test-debugcomplete.t
--- a/tests/test-debugcomplete.t
+++ b/tests/test-debugcomplete.t
@@ -75,6 +75,7 @@ Show debug commands if there are no othe
   debugdata
   debugdate
   debugfsinfo
+  debugignore
   debugindex
   debugindexdot
   debuginstall
@@ -214,6 +215,7 @@ Show all commands + options
   debugdata: 
   debugdate: extended
   debugfsinfo: 
+  debugignore: 
   debugindex: format
   debugindexdot: 
   debuginstall: 
diff --git a/tests/test-hgignore.t b/tests/test-hgignore.t
--- a/tests/test-hgignore.t
+++ b/tests/test-hgignore.t
@@ -120,3 +120,5 @@ Check it does not ignore the current dir
   $ hg status .
   A b.o
 
+  $ hg debugignore
+  (?:(?:|.*/)[^/]*(?:/|$))