Add the following code under the top PHP opening tag of wp-config.php.
<?php
if (!session_id()) {
session_start();
}
...
We can now make use of the $_SESSION[] in WordPress. The reason of putting the session_start() in wp-config.php is because this configuration file will not be overwritten during a WordPress update.
Thanks Frank Verhoeven.
Done =)
Reference: Frank Verhoeven – Using Sessions in WordPress
Updated @ 2012-08-02: Please note that their maybe security issue of using the PHP session. For more information, please refer to the following link.
PHP $_SESSION variables
Eureka! 
Why not put on functions.php of your theme?
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if functions.php is also included at application start up, i guess it should be ok too.
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Hello friends, this does not work, because WP is unsetting all global variables in the wp-settings.php file.
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I tried the above approach in WordPress 2.8.6.
which version are u using?
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hi i have tried this as wella s putting it in the functions.php, as well as adding it to the wp_unregister_globals array….but none seems to work for me .Instead they crash my website i end up getting a blank screen. Everything reverts to normal when i remove it from the config.php or functions.php
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What wordpress version are u using?
Have you tried to add it to wp-config.php instead of config.php and functions.php?
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http://support.wpengine.com/php-session-variables/
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Thanks for the link. =)
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