Congenital multicystic kidney is the most common cause of an abdominal mass in infancy. The disease may persist into the adult life and be incidentally discovered. Although it became a distinct pathologic entity in 1955, clinical and roentgenologic diagnosis of a congenital multicystic kidney could not be made with certainty. This is because the diagnostic features consisting of a unilateral nonfunctioning kidney with or without a palpable flank mass are also observed in Wilms’ tumor in children and renal cell carcinoma in adults, congenital unilateral hydronephrosis, renal vein thrombosis, renal artery occlusion, renal xanthogranulomatous pyelonephritis and renal agenesis. In view of lack of a diagnostic procedure to make an accurate diagnosis, these patients have been subjected to surgical exploration to confirm the clinical suspicion of congenital multicystic kidney, so as to make certain that one is not dealing with the more serious or malignant renal diseases considered in the differential diagnosis....