EXAMPLES.txt says concerning "Output" frontend: if ($cache->start($id)) { // cache is not hit ! // Output you want to cache for ($i=0;$i<10000;$i++) { echo($i); } // store "captured" output into cache $cache->end(); } But Zend_Cache_Frontend_Output::start() method returns true when cache hit and false otherwise, so the function or example should be changed.