diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -372,6 +372,9 @@ coreconfigitem('devel', 'user.obsmarker'
 coreconfigitem('devel', 'warn-config-unknown',
     default=None,
 )
+coreconfigitem('devel', 'debug.extensions',
+    default=False,
+)
 coreconfigitem('devel', 'debug.peer-request',
     default=False,
 )
diff --git a/mercurial/extensions.py b/mercurial/extensions.py
--- a/mercurial/extensions.py
+++ b/mercurial/extensions.py
@@ -123,10 +123,11 @@ def _importext(name, path=None, reportfu
 def _reportimporterror(ui, err, failed, next):
     # note: this ui.debug happens before --debug is processed,
     #       Use --config ui.debug=1 to see them.
-    ui.debug('could not import %s (%s): trying %s\n'
-             % (failed, stringutil.forcebytestr(err), next))
-    if ui.debugflag:
-        ui.traceback()
+    if ui.configbool('devel', 'debug.extensions'):
+        ui.debug('could not import %s (%s): trying %s\n'
+                 % (failed, stringutil.forcebytestr(err), next))
+        if ui.debugflag:
+            ui.traceback()
 
 def _rejectunicode(name, xs):
     if isinstance(xs, (list, set, tuple)):
diff --git a/tests/test-bad-extension.t b/tests/test-bad-extension.t
--- a/tests/test-bad-extension.t
+++ b/tests/test-bad-extension.t
@@ -72,10 +72,9 @@ names of extensions failed to load can b
   $ hg --config extensions.badexts=showbadexts.py showbadexts 2>&1 | grep '^BADEXTS'
   BADEXTS: badext badext2
 
-show traceback for ImportError of hgext.name if debug is set
-(note that --debug option isn't applied yet when loading extensions)
+show traceback for ImportError of hgext.name if devel.debug.extensions is set
 
-  $ (hg help help --traceback --config ui.debug=yes 2>&1) \
+  $ (hg help help --traceback --debug --config devel.debug.extensions=yes 2>&1) \
   > | grep -v '^ ' \
   > | egrep 'extension..[^p]|^Exception|Traceback|ImportError|not import'
   *** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow