diff --git a/Source/cmGlobalXCodeGenerator.cxx b/Source/cmGlobalXCodeGenerator.cxx
index fd9dacd1a..cde02b735 100644
--- a/Source/cmGlobalXCodeGenerator.cxx
+++ b/Source/cmGlobalXCodeGenerator.cxx
@@ -489,12 +489,34 @@ void cmGlobalXCodeGenerator::ClearXCodeObjects()
     delete this->XCodeObjects[i];
     }
   this->XCodeObjects.clear();
+  this->XCodeObjectIDs.clear();
   this->GroupMap.clear();
   this->GroupNameMap.clear();
   this->TargetGroup.clear();
   this->FileRefs.clear();
 }
 
+//----------------------------------------------------------------------------
+void cmGlobalXCodeGenerator::addObject(cmXCodeObject *obj)
+{
+  if(obj->GetType() == cmXCodeObject::OBJECT)
+    {
+    cmStdString id = obj->GetId();
+
+    // If this is a duplicate id, it's an error:
+    //
+    if(this->XCodeObjectIDs.count(id))
+      {
+      cmSystemTools::Error(
+        "Xcode generator: duplicate object ids not allowed");
+      }
+
+    this->XCodeObjectIDs.insert(id);
+    }
+
+  this->XCodeObjects.push_back(obj);
+}
+
 //----------------------------------------------------------------------------
 cmXCodeObject*
 cmGlobalXCodeGenerator::CreateObject(cmXCodeObject::PBXType ptype)
@@ -508,7 +530,7 @@ cmGlobalXCodeGenerator::CreateObject(cmXCodeObject::PBXType ptype)
     {
     obj = new cmXCode21Object(ptype, cmXCodeObject::OBJECT);
     }
-  this->XCodeObjects.push_back(obj);
+  this->addObject(obj);
   return obj;
 }
 
@@ -517,7 +539,7 @@ cmXCodeObject*
 cmGlobalXCodeGenerator::CreateObject(cmXCodeObject::Type type)
 {
   cmXCodeObject* obj = new cmXCodeObject(cmXCodeObject::None, type);
-  this->XCodeObjects.push_back(obj);
+  this->addObject(obj);
   return obj;
 }
 
@@ -2040,6 +2062,9 @@ cmGlobalXCodeGenerator::CreateUtilityTarget(cmTarget& cmtarget)
       }
     }
 
+  target->SetId(this->GetOrCreateId(
+    cmtarget.GetName(), target->GetId()).c_str());
+
   return target;
 }
 
@@ -2188,6 +2213,8 @@ cmGlobalXCodeGenerator::CreateXCodeTarget(cmTarget& cmtarget,
     target->AddAttribute("productType", this->CreateString(productType));
     }
   target->SetTarget(&cmtarget);
+  target->SetId(this->GetOrCreateId(
+    cmtarget.GetName(), target->GetId()).c_str());
   return target;
 }
 
@@ -2210,6 +2237,26 @@ cmXCodeObject* cmGlobalXCodeGenerator::FindXCodeTarget(cmTarget* t)
   return 0;
 }
 
+//----------------------------------------------------------------------------
+std::string cmGlobalXCodeGenerator::GetOrCreateId(const char* name,
+                                                  const char* id)
+{
+  std::string guidStoreName = name;
+  guidStoreName += "_GUID_CMAKE";
+  const char* storedGUID =
+    this->CMakeInstance->GetCacheDefinition(guidStoreName.c_str());
+
+  if(storedGUID)
+    {
+    return storedGUID;
+    }
+
+  this->CMakeInstance->AddCacheEntry(guidStoreName.c_str(),
+    id, "Stored Xcode object GUID", cmCacheManager::INTERNAL);
+
+  return id;
+}
+
 //----------------------------------------------------------------------------
 void cmGlobalXCodeGenerator::AddDependTarget(cmXCodeObject* target,
                                              cmXCodeObject* dependTarget)
@@ -2739,6 +2786,12 @@ void cmGlobalXCodeGenerator
 
   this->RootObject = this->CreateObject(cmXCodeObject::PBXProject);
   this->RootObject->SetComment("Project object");
+
+  std::string project_id = "PROJECT_";
+  project_id += root->GetMakefile()->GetProjectName();
+  this->RootObject->SetId(this->GetOrCreateId(
+    project_id.c_str(), this->RootObject->GetId()).c_str());
+
   group = this->CreateObject(cmXCodeObject::ATTRIBUTE_GROUP);
   this->RootObject->AddAttribute("mainGroup",
                              this->CreateObjectReference(mainGroup));
@@ -3137,6 +3190,11 @@ cmGlobalXCodeGenerator::OutputXCodeProject(cmLocalGenerator* root,
     }
   this->WriteXCodePBXProj(fout, root, generators);
   this->ClearXCodeObjects();
+
+  // Since this call may have created new cache entries, save the cache:
+  //
+  root->GetMakefile()->GetCacheManager()->SaveCache(
+    root->GetMakefile()->GetHomeOutputDirectory());
 }
 
 //----------------------------------------------------------------------------
diff --git a/Source/cmGlobalXCodeGenerator.h b/Source/cmGlobalXCodeGenerator.h
index 39a5fd722..fa55ff08a 100644
--- a/Source/cmGlobalXCodeGenerator.h
+++ b/Source/cmGlobalXCodeGenerator.h
@@ -123,6 +123,8 @@ private:
                                 );
   
   cmXCodeObject* FindXCodeTarget(cmTarget*);
+  std::string GetOrCreateId(const char* name, const char* id);
+
   // create cmXCodeObject from these functions so that memory can be managed
   // correctly.  All objects created are stored in this->XCodeObjects.
   cmXCodeObject* CreateObject(cmXCodeObject::PBXType ptype);
@@ -197,9 +199,11 @@ protected:
 
   unsigned int XcodeVersion;
   std::string VersionString;
+  std::set<cmStdString> XCodeObjectIDs;
   std::vector<cmXCodeObject*> XCodeObjects;
   cmXCodeObject* RootObject;
 private:
+  void addObject(cmXCodeObject *obj);
   std::string PostBuildMakeTarget(std::string const& tName,
                                   std::string const& configName);
   cmXCodeObject* MainGroupChildren;
diff --git a/Source/cmXCodeObject.cxx b/Source/cmXCodeObject.cxx
index 30e5076c4..30ade9637 100644
--- a/Source/cmXCodeObject.cxx
+++ b/Source/cmXCodeObject.cxx
@@ -12,6 +12,8 @@
 #include "cmXCodeObject.h"
 #include "cmSystemTools.h"
 
+#include <CoreFoundation/CoreFoundation.h> // CFUUIDCreate
+
 //----------------------------------------------------------------------------
 const char* cmXCodeObject::PBXTypeNames[] = {
     "PBXGroup", "PBXBuildStyle", "PBXProject", "PBXHeadersBuildPhase", 
@@ -39,35 +41,35 @@ cmXCodeObject::cmXCodeObject(PBXType ptype, Type type)
   this->PBXTargetDependencyValue = 0;
   this->Target = 0;
   this->Object =0;
-  
+
   this->IsA = ptype;
+
   if(type == OBJECT)
     {
-    cmOStringStream str;
-    str << (void*)this;
-    str << (void*)this;
-    str << (void*)this;
-    this->Id = str.str();
+    // Set the Id of an Xcode object to a unique string for each instance.
+    // However the Xcode user file references certain Ids: for those cases,
+    // override the generated Id using SetId().
+    //
+    char cUuid[40] = {0};
+    CFUUIDRef uuid = CFUUIDCreate(kCFAllocatorDefault);
+    CFStringRef s = CFUUIDCreateString(kCFAllocatorDefault, uuid);
+    CFStringGetCString(s, cUuid, sizeof(cUuid), kCFStringEncodingUTF8);
+    this->Id = cUuid;
+    CFRelease(s);
+    CFRelease(uuid);
     }
   else
     {
-    this->Id = 
-      "Temporary cmake object, should not be refered to in xcode file";
-    }
-  cmSystemTools::ReplaceString(this->Id, "0x", "");
-  this->Id = cmSystemTools::UpperCase(this->Id);
-  if(this->Id.size() < 24)
-    {
-    int diff = 24 - this->Id.size();
-    for(int i =0; i < diff; ++i)
-      {
-      this->Id += "0";
-      }
+    this->Id =
+      "Temporary cmake object, should not be referred to in Xcode file";
     }
+
+  cmSystemTools::ReplaceString(this->Id, "-", "");
   if(this->Id.size() > 24)
     {
-    this->Id = this->Id.substr(0,24);
+    this->Id = this->Id.substr(0, 24);
     }
+
   this->TypeValue = type;
   if(this->TypeValue == OBJECT)
     {
diff --git a/Source/cmXCodeObject.h b/Source/cmXCodeObject.h
index 369fe669d..2fb96f30e 100644
--- a/Source/cmXCodeObject.h
+++ b/Source/cmXCodeObject.h
@@ -83,6 +83,10 @@ public:
     {
       return this->Id.c_str();
     }
+  void SetId(const char* id)
+    {
+      this->Id = id;
+    }
   cmTarget* GetTarget()
     {
       return this->Target;