Bilateral hydronephrosis is the medical condition that indicates the enlargement of the pelvis and other organs responsible for collecting urine. The word bilateral indicates both the sides.

Bilateral hydronephrosis is mainly caused when the urine fails to drain from the kidneys to the ureter and then into the bladder. The term bilateral hydronephrosis is not exactly a diseased condition; it is instead a condition occurring due to underlying disease that beholds the urine from following its original path to reach the bladder. This disease may be caused by obstruction of bladder outlet, acute and chronic bilateral obstructive uropathy, posterior ureteral valves, neurogenic bladder, uteropelvic junction obstruction, prune belly syndrome, and vesicoureteric reflux.