diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -1457,7 +1457,7 @@ def heads(ui, repo, *branchrevs, **opts)
         displayer.show(ctx)
     displayer.close()
 
-def help_(ui, name=None, with_version=False):
+def help_(ui, name=None, with_version=False, unknowncmd=False):
     """show help for a given topic or a help overview
 
     With no arguments, print a list of commands with short help messages.
@@ -1490,7 +1490,7 @@ def help_(ui, name=None, with_version=Fa
             ui.write('\n')
 
         try:
-            aliases, entry = cmdutil.findcmd(name, table, False)
+            aliases, entry = cmdutil.findcmd(name, table, strict=unknowncmd)
         except error.AmbiguousCommand, inst:
             # py3k fix: except vars can't be used outside the scope of the
             # except block, nor can be used inside a lambda. python issue4617
@@ -1501,7 +1501,8 @@ def help_(ui, name=None, with_version=Fa
 
         # check if it's an invalid alias and display its error if it is
         if getattr(entry[0], 'badalias', False):
-            entry[0](ui)
+            if not unknowncmd:
+                entry[0](ui)
             return
 
         # synopsis
@@ -1592,10 +1593,13 @@ def help_(ui, name=None, with_version=Fa
     def helpext(name):
         try:
             mod = extensions.find(name)
+            doc = gettext(mod.__doc__) or _('no help text available')
         except KeyError:
-            raise error.UnknownCommand(name)
-
-        doc = gettext(mod.__doc__) or _('no help text available')
+            mod = None
+            doc = extensions.disabledext(name)
+            if not doc:
+                raise error.UnknownCommand(name)
+
         if '\n' not in doc:
             head, tail = doc, ""
         else:
@@ -1605,17 +1609,36 @@ def help_(ui, name=None, with_version=Fa
             ui.write(minirst.format(tail, textwidth))
             ui.status('\n\n')
 
-        try:
-            ct = mod.cmdtable
-        except AttributeError:
-            ct = {}
-
-        modcmds = set([c.split('|', 1)[0] for c in ct])
-        helplist(_('list of commands:\n\n'), modcmds.__contains__)
+        if mod:
+            try:
+                ct = mod.cmdtable
+            except AttributeError:
+                ct = {}
+            modcmds = set([c.split('|', 1)[0] for c in ct])
+            helplist(_('list of commands:\n\n'), modcmds.__contains__)
+        else:
+            ui.write(_('use "hg help extensions" for information on enabling '
+                       'extensions\n'))
+
+    def helpextcmd(name):
+        cmd, ext, mod = extensions.disabledcmd(name, ui.config('ui', 'strict'))
+        doc = gettext(mod.__doc__).splitlines()[0]
+
+        msg = help.listexts(_("'%s' is provided by the following "
+                              "extension:") % cmd, {ext: doc}, len(ext),
+                            indent=4)
+        ui.write(minirst.format(msg, textwidth))
+        ui.write('\n\n')
+        ui.write(_('use "hg help extensions" for information on enabling '
+                   'extensions\n'))
 
     if name and name != 'shortlist':
         i = None
-        for f in (helptopic, helpcmd, helpext):
+        if unknowncmd:
+            queries = (helpextcmd,)
+        else:
+            queries = (helptopic, helpcmd, helpext, helpextcmd)
+        for f in queries:
             try:
                 f(name)
                 i = None
diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -93,7 +93,12 @@ def _runcatch(ui, args):
         ui.warn(_("killed!\n"))
     except error.UnknownCommand, inst:
         ui.warn(_("hg: unknown command '%s'\n") % inst.args[0])
-        commands.help_(ui, 'shortlist')
+        try:
+            # check if the command is in a disabled extension
+            # (but don't check for extensions themselves)
+            commands.help_(ui, inst.args[0], unknowncmd=True)
+        except error.UnknownCommand:
+            commands.help_(ui, 'shortlist')
     except util.Abort, inst:
         ui.warn(_("abort: %s\n") % inst)
     except ImportError, inst:
@@ -218,6 +223,11 @@ class cmdalias(object):
             def fn(ui, *args):
                 ui.warn(_("alias '%s' resolves to unknown command '%s'\n") \
                             % (self.name, cmd))
+                try:
+                    # check if the command is in a disabled extension
+                    commands.help_(ui, cmd, unknowncmd=True)
+                except error.UnknownCommand:
+                    pass
                 return 1
             self.fn = fn
             self.badalias = True
diff --git a/mercurial/extensions.py b/mercurial/extensions.py
--- a/mercurial/extensions.py
+++ b/mercurial/extensions.py
@@ -6,7 +6,7 @@
 # GNU General Public License version 2 or any later version.
 
 import imp, os
-import util, cmdutil, help
+import util, cmdutil, help, error
 from i18n import _, gettext
 
 _extensions = {}
@@ -131,8 +131,9 @@ def wrapfunction(container, funcname, wr
     setattr(container, funcname, wrap)
     return origfn
 
-def _disabledpaths():
-    '''find paths of disabled extensions. returns a dict of {name: path}'''
+def _disabledpaths(strip_init=False):
+    '''find paths of disabled extensions. returns a dict of {name: path}
+    removes /__init__.py from packages if strip_init is True'''
     import hgext
     extpath = os.path.dirname(os.path.abspath(hgext.__file__))
     try: # might not be a filesystem path
@@ -150,6 +151,8 @@ def _disabledpaths():
             path = os.path.join(extpath, e, '__init__.py')
             if not os.path.exists(path):
                 continue
+            if strip_init:
+                path = os.path.dirname(path)
         if name in exts or name in _order or name == '__init__':
             continue
         exts[name] = path
@@ -191,6 +194,53 @@ def disabled():
 
     return exts, maxlength
 
+def disabledext(name):
+    '''find a specific disabled extension from hgext. returns desc'''
+    paths = _disabledpaths()
+    if name in paths:
+        return _disabledhelp(paths[name])
+
+def disabledcmd(cmd, strict=False):
+    '''import disabled extensions until cmd is found.
+    returns (cmdname, extname, doc)'''
+
+    paths = _disabledpaths(strip_init=True)
+    if not paths:
+        raise error.UnknownCommand(cmd)
+
+    def findcmd(cmd, name, path):
+        try:
+            mod = loadpath(path, 'hgext.%s' % name)
+        except Exception:
+            return
+        try:
+            aliases, entry = cmdutil.findcmd(cmd,
+                getattr(mod, 'cmdtable', {}), strict)
+        except (error.AmbiguousCommand, error.UnknownCommand):
+            return
+        for c in aliases:
+            if c.startswith(cmd):
+                cmd = c
+                break
+        else:
+            cmd = aliases[0]
+        return (cmd, name, mod)
+
+    # first, search for an extension with the same name as the command
+    path = paths.pop(cmd, None)
+    if path:
+        ext = findcmd(cmd, cmd, path)
+        if ext:
+            return ext
+
+    # otherwise, interrogate each extension until there's a match
+    for name, path in paths.iteritems():
+        ext = findcmd(cmd, name, path)
+        if ext:
+            return ext
+
+    raise error.UnknownCommand(cmd)
+
 def enabled():
     '''return a dict of {name: desc} of extensions, and the max name length'''
     exts = {}
diff --git a/mercurial/help.py b/mercurial/help.py
--- a/mercurial/help.py
+++ b/mercurial/help.py
@@ -42,13 +42,14 @@ def moduledoc(file):
 
     return ''.join(result)
 
-def listexts(header, exts, maxlength):
+def listexts(header, exts, maxlength, indent=1):
     '''return a text listing of the given extensions'''
     if not exts:
         return ''
     result = '\n%s\n\n' % header
     for name, desc in sorted(exts.iteritems()):
-        result += ' %-*s %s\n' % (maxlength + 2, ':%s:' % name, desc)
+        result += '%s%-*s %s\n' % (' ' * indent, maxlength + 2,
+                                   ':%s:' % name, desc)
     return result
 
 def extshelp():
diff --git a/tests/test-extension b/tests/test-extension
--- a/tests/test-extension
+++ b/tests/test-extension
@@ -153,3 +153,27 @@ echo "hgext/mq=" >> $HGRCPATH
 
 echo % show extensions
 hg debugextensions
+
+echo '% disabled extension commands'
+HGRCPATH=
+hg help email
+hg qdel
+hg churn
+echo '% disabled extensions'
+hg help churn
+hg help patchbomb
+echo '% broken disabled extension and command'
+mkdir hgext
+echo > hgext/__init__.py
+cat > hgext/broken.py <<EOF
+"broken extension'
+EOF
+TMPPYTHONPATH="$PYTHONPATH"
+PYTHONPATH="`pwd`:$PYTHONPATH"
+export PYTHONPATH
+hg help broken
+hg help foo > /dev/null
+PYTHONPATH="$TMPPYTHONPATH"
+export PYTHONPATH
+
+exit 0
diff --git a/tests/test-extension.out b/tests/test-extension.out
--- a/tests/test-extension.out
+++ b/tests/test-extension.out
@@ -96,3 +96,33 @@ global options:
 % show extensions
 debugissue811
 mq
+% disabled extension commands
+'email' is provided by the following extension:
+
+    patchbomb  command to send changesets as (a series of) patch emails
+
+use "hg help extensions" for information on enabling extensions
+hg: unknown command 'qdel'
+'qdelete' is provided by the following extension:
+
+    mq  manage a stack of patches
+
+use "hg help extensions" for information on enabling extensions
+hg: unknown command 'churn'
+'churn' is provided by the following extension:
+
+    churn  command to display statistics about repository history
+
+use "hg help extensions" for information on enabling extensions
+% disabled extensions
+churn extension - command to display statistics about repository history
+
+use "hg help extensions" for information on enabling extensions
+patchbomb extension - command to send changesets as (a series of) patch emails
+
+use "hg help extensions" for information on enabling extensions
+% broken disabled extension and command
+broken extension - (no help text available)
+
+use "hg help extensions" for information on enabling extensions
+hg: unknown command 'foo'