Zend_Session::expireSessionCookie method will fail when it is called on the same page as a new session is created. Example: a new user comes to my website, and I start a session using Zend_Session::start(), there will be no $_COOKIE[session_name()], so this test will fail, if (isset($_COOKIE[session_name()])) { ... } which leaves a case when after I have called Zend_Session::expireSessionCookie, the user still has a session cookie! I suggest to replace the if test w/ the following if (isset($_COOKIE[session_name()]) || self::$_sessionStarted) { ... } } which solved my issue