Amniotic fluid alpha-fetoprotein has been associated with various congenital anomalies. A diagnosis in utero of urinary obstruction associated with elevated alpha-fetoprotein is reported. Subsequent fulguration of type I posterior urethral valves was done. A possible mechanism for elevated alpha-fetoprotein with obstructive uropathy in utero is discussed. Pediatrics 66:537-539, 1980; alpha-fetoprotein, amniotic fluid, obstructive uropathy, posterior urethral valves, polyhydramnios.