Abstract
A caliceal diverticulum is a rare entity in children. Its etiology is closely associated with that of ureteropelvic junction malformations and renal dysplasia. We herein present a case of these complex disorders in an infant. A renal cyst and hydronephrosis were found in the left kidney during the fetal period. The postnatal diagnosis was hydronephrosis due to ureteropelvic junction obstruction and a caliceal diverticulum in the left dysplastic kidney. Although left renal function was severely decreased, the patient had no symptoms. Therefore, we did not perform surgical treatment. At the time of this writing, the patient was 3 years 8 months old and had developed no symptoms.