since I had everything else correctly setup. Make sure your php.ini file is read at all. I had the problem that on a Windows 2003 Server the php.ini was not read, so only default values were used resulting in no extension modules to work, because they do not reside in C:\PHP5 but in D:\PHP\ext. The output of phpinfo() told me the "Configuration File (php.ini) Path" was "C:\WINDOWS". Well this sounded good to me because I had copied the php.ini file from D:\PHP to C:\WINDOWS. But a path to a directory as a value of "Configuration File (php.ini) Path" instead of the full path to the php.ini file you expect to be read means that NO php.ini file could be found so that the default values are used. What fixed the problem was adding a System variable "PHPRC" set to the path to the directory where the php.ini file is to be found. After rebooting the Server everything was fine - the extension_dir was set correctly and after all I succeeded in connecting to my MySQL-Database-Server. :-) 7. Special note on libmysql.dll and problems getting MySQL to work: - You may have copied over this file into your Windows/System32 (or WINNT/System32 for me) to get mysql to work in the past.  If so, replace it with the most recent version you get with the upgrade (in top dir). - If this is a fresh install, copy the libmysql.dll into your System32 folder. If you are having trouble getting extensions to run