1 in 5000 births.  Mostly failure of Wolffian duct development, rarely failure of urethral canalisation.

2/3 detected antenatally, with distended bladder. If missed, then present with urinary tract infection, abnormal voiding (dribble rather than fountain!) else incontinence (if toilet trained, of course).

Later detrusor failure, tubular dysfunction, renal failure.