Prenatal diagnosis of left multicystic dysplastic kidney (MCDK) and ureterocele was made in a male fetus at 24-week gestation. The initial postnatal course was uneventful. At 4 weeks of age, he developed urosepsis and respiratory distress. Ultrasound and MR urogram demonstrated a duplicated left collecting system with massive upper pole dilation and left ureterocele. Ureterocele puncture was performed, though failed to improve the clinical picture. Upper pole nephrostomy tube placement and subsequent upper pole heminephrectomy were performed and symptoms resolved. This case highlights the complexity of diagnosing and managing congenital anomalies of the kidney and urinary tract (CAKUT).