diff --git a/checkin_notes b/checkin_notes
index b1993209aa..e9ee541255 100644
--- a/checkin_notes
+++ b/checkin_notes
@@ -7317,3 +7317,11 @@ Charlie 14 Oct 2010
     
     client/
         cs_scheduler.cpp
+
+Rom    14 Oct 2010
+    - MGR: Check for a duplicate instance much earlier in the initialization
+        cycle, before any window or document creation.  Prevents rapid window
+        creation and then destruction.
+        
+    clientgui/
+        BOINCGUIApp.cpp, .h
diff --git a/clientgui/BOINCGUIApp.cpp b/clientgui/BOINCGUIApp.cpp
index b85cbd58ec..d4958d8ac6 100644
--- a/clientgui/BOINCGUIApp.cpp
+++ b/clientgui/BOINCGUIApp.cpp
@@ -381,6 +381,13 @@ bool CBOINCGUIApp::OnInit() {
     }
 #endif
 
+    // Detect if BOINC Manager is already running, if so, bring it into the
+    // foreground and then exit.
+    if (!m_bMultipleInstancesOK) {
+        if (DetectDuplicateInstance()) {
+            return false;
+        }
+    }
 
     // Initialize the main document
     m_pDocument = new CMainDocument();
@@ -652,6 +659,23 @@ void CBOINCGUIApp::DetectAccessibilityEnabled() {
 }
 
 
+///
+/// Detect if another instance of this application is running.
+//  Returns true if there is, otherwise false
+///
+bool CBOINCGUIApp::DetectDuplicateInstance() {
+#ifdef __WXMSW__
+    HWND hWnd = ::FindWindow(NULL, m_pSkinManager->GetAdvanced()->GetApplicationName().c_str());
+    if (hWnd) {
+        ::ShowWindow(hWnd, SW_SHOW);
+        ::SetForegroundWindow(hWnd);
+        return true;
+    }
+#endif
+    return false;
+}
+
+
 ///
 /// Determines what name BOINC Manager is called.
 ///
diff --git a/clientgui/BOINCGUIApp.h b/clientgui/BOINCGUIApp.h
index f7c86dc100..e1a25b2899 100644
--- a/clientgui/BOINCGUIApp.h
+++ b/clientgui/BOINCGUIApp.h
@@ -60,6 +60,7 @@ protected:
 
     void                DetectDisplayInfo();
     void                DetectAccessibilityEnabled();
+    bool                DetectDuplicateInstance();
     void                DetectExecutableName();
     void                DetectRootDirectory();
     void                DetectDataDirectory();