Urorectal septum malformation sequences are rare congenital malformations. We report a case of persistent cloaca prenatally diagnosed at 26 weeks of gestation in 1 of a set of discordant monozygotic twins. The affected fetus at birth had a phallus-like structure, bladder outlet obstruction, an imperforate anus, and uterine distension. Diverting colostomy, vesicostomy, and percutaneous colpostomy tube were initially placed before definitive posterior sagittal anorectovaginoplasty was completed. A cloacal anomaly occurring in only 1 of a set of monozygotic twins is an exceedingly rare event.