<prompt> A most common cause of urinary obstruction in a male infant isAnterior urethral valvesPosterior urethral valvesStoneStricture  <response>: The most common cause of severe obstructive uropathy in children is posterior urethral valves.___ NelsonPosterior urethral valvesThese are symmetrical folds of urothelium extending distally from prostatic urethra to external urinary sphincter.It most commonly lies just distal to the verumontanum or at the verumontanum.It occurs only in males.It behaves as flap valves so, although urine does not flow normally a urethral catheter can be passed without difficulty.Sometimes, the valves are incomplete and the patient remains without symptoms until adolescence or adulthood.Approximately 30 of patients experience end-stage renal diseaseVesicoureteral reflux occurs in 50 of patients.Diagnosis is made byVoiding cystourethrogramEndoscopyBoth of these investigations clearly depict the site of obstruction.The diagnosis can be established prenatally by ultrasound. 