RESUMO
Giant hydronephrosis is an ultimate rare urologic entity; even rarer when it is secondary to a duplex collecting system. Duplex collecting system is a common urologic anomaly with a wide range of clinical symptoms and a variety of associated urologic abnormalities such as an ectopic ureter, ureterocele, vesicoureteral reflux and ureteropelvic junction obstruction. This report presents a case of an 8-year-old boy who had a bilateral duplex collecting system that was revealed accidentally by a bilateral severe hydronephrosis. The duplication was complete on the left side and partial on the right with a right ectopic ureteral orifice, in addition to a bilateral vesicoureteral reflux. The vesicoureteral reflux retreated completely in the left side after using a urethral catheter for 6 months, while the decision of performing a surgical operation for the right side was made.