We describe the case of a 10-day-old term infant with 47,XXY, in association with posterior urethral valves, a right ectopic ureter, a right dysplastic kidney, left hydronephrosis, cryptorchidism, and encephalomalacia. The renal anomaly was diagnosed prenatally by ultrasonography, and additional evaluation was performed after birth. Urinary tract anomalies are uncommon in Klinefelter syndrome. Unilateral and bilateral renal agenesis have been described. We describe, to our knowledge, the first case of posterior urethral valves, ectopic ureter, and encephalomalacia in association with 47,XXY.