Kidney Shot is a core rogue ability learned at level 40. It is used to stun monsters or enemy players, preventing them from escaping or causing further damage. Duration is dependent upon the number of combo points used.
Key ability of a full stunlock, Kidney Shot allows you to keep a target stunned while dishing out major damage to them.
Against a PvP target try to wait a second or two after the cooldown is up before using another Kidney Shot. If you Kidney Shot the target within 15 seconds of the last one (after 21 seconds) the effect is reduced to 50%.
Patch 3.0.8 (2009-01-20): This ability now has diminishing returns against all other stuns.