[Kidney calculus episode in a supernumerary 3rd kidney].

Supernumerary kidney is a rare renal anomaly. As a distinct encapsulated parenchymatous mass, this free accessory organ has a separate blood supply and excretory duct system. We report on a patient who presented with an acute episode of abdominopelvic pain, secondary to hydronephrosis of a third kidney, situated in the pelvis behind the bladder. Modern diagnostic methods assisted in the conservative management of this well functioning third kidney.