From 1985 to 1993, 33 female and 4 male patients 0 to 3 years old presented with abnormal complete duplex systems of whom 25 had a prenatal diagnosis of hydronephrosis. Diagnosis in 40 ureteral moieties included ureteroceles in 10, ectopic ureteral insertions with reflux and obstruction in 17, and refluxing lower ureters in 13. Of 40 renal units only 6 (15%) required upper pole moiety ablation for pyelonephritis or nonfunction. None of the ablated renal tissue showed evidence of dysplasia. With the advent of prenatal diagnosis and minimal surgical intervention complete duplex anomalous urinary systems can be salvaged with preservation of altered renal units.