diff --git a/gui/__init__.py b/gui/__init__.py
index 73e0db8..909265c 100644
--- a/gui/__init__.py
+++ b/gui/__init__.py
@@ -16,3 +16,7 @@
 import os.path
 
 self_dir = os.path.abspath(os.path.dirname(__file__))
+
+# Import anything that defines a command or parameter.
+import gui.commands
+import gui.toplevel
diff --git a/gui/commands.py b/gui/commands.py
index ae41c40..6b89e07 100644
--- a/gui/commands.py
+++ b/gui/commands.py
@@ -28,6 +28,7 @@ class GuiSourceCommand(gdb.Command):
                                                gdb.COMMAND_SUPPORT)
 
     def invoke(self, arg, from_tty):
+        self.dont_repeat()
         gui.startup.start_gtk()
         gui.startup.send_to_gtk(gui.source.SourceWindow)
 
diff --git a/gui/source.py b/gui/source.py
index 3a57562..488bd7a 100644
--- a/gui/source.py
+++ b/gui/source.py
@@ -17,8 +17,10 @@
 
 import gdb
 from gui.invoker import Invoker
+from gui.toplevel import Toplevel
 import gui.startup
 import os.path
+import gui.toplevel
 
 from gi.repository import Gtk, GtkSource, GObject
 
@@ -140,8 +142,10 @@ class LRUHandler:
 
 lru_handler = LRUHandler()
 
-class SourceWindow:
+class SourceWindow(Toplevel):
     def __init__(self):
+        super(SourceWindow, self).__init__()
+
         self.frame = None
 
         self.do_step = Invoker("step")
diff --git a/gui/toplevel.py b/gui/toplevel.py
new file mode 100644
index 0000000..3731f38
--- /dev/null
+++ b/gui/toplevel.py
@@ -0,0 +1,93 @@
+# Copyright (C) 2013 Tom Tromey <tom@tromey.com>
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Toplevel handling.
+
+import gdb
+import gui.startup
+import threading
+
+class _ToplevelState(object):
+    def __init__(self):
+        # This lock must be held when using the other globals here.
+        self.toplevel_lock = threading.Lock()
+        self.next_toplevel = 1
+        self.toplevels = {}
+
+    def add(self, obj):
+        with self.toplevel_lock:
+            obj.number = self.next_toplevel
+            self.next_toplevel = self.next_toplevel + 1
+            self.toplevels[obj.number] = obj
+
+    def remove(self, obj):
+        with self.toplevel_lock:
+            del self.toplevels[obj.number]
+
+    def get(self, winno):
+        window = None
+        with self.toplevel_lock:
+            if winno in self.toplevels:
+                window = self.toplevels[winno]
+        return window
+
+    def display(self):
+        with self.toplevel_lock:
+            if len(self.toplevels) == 0:
+                print "No windows"
+                return
+
+            print ' Num    Name'
+            for winno in range(1, self.next_toplevel):
+                if winno in self.toplevels:
+                    window = self.toplevels[winno]
+                    print ' %3d    %s' % (window.number,
+                                          window.window.get_title())
+
+_toplevel_state = _ToplevelState()
+
+class Toplevel(object):
+    def __init__(self):
+        _toplevel_state.add(self)
+        # The subclass must set this.
+        self.window = None
+
+    def destroy(self):
+        _toplevel_state.remove(self)
+        gui.startup.send_to_gtk(self.window.destroy)
+
+class InfoWindowsCommand(gdb.Command):
+    def __init__(self):
+        super(InfoWindowsCommand, self).__init__('info windows',
+                                                 gdb.COMMAND_SUPPORT)
+
+    def invoke(self, arg, from_tty):
+        self.dont_repeat()
+        _toplevel_state.display()
+
+class DeleteWindowsCommand(gdb.Command):
+    def __init__(self):
+        super(DeleteWindowsCommand, self).__init__('delete window',
+                                                   gdb.COMMAND_SUPPORT)
+
+    def invoke(self, arg, from_tty):
+        self.dont_repeat()
+        winno = int(arg)
+        window = _toplevel_state.get(winno)
+        if window is not None:
+            window.destroy()
+
+InfoWindowsCommand()
+DeleteWindowsCommand()