Cloacal malformation occurs in approximately 1 in 50,000 live female births. Prenatal ultrasound may lead to the diagnosis in selected cases. We report an unusual case of prenatally detected single-system hydronephrosis with a nonvisible bladder and worsening oligohydramnios. Labor was induced at 35 weeks’ estimated gestational age. On physical examination, a single perineal opening was noted consistent with cloaca. Endoscopy revealed an obstructed ectopic ureter at the level of the sphincter, an undeveloped bladder and vagina, and a fistula to the rectum. A low loop cutaneous ureterostomy and right upper quadrant loop colostomy were performed. The absence of a typical fluid-filled pelvic structure may confound the prenatal diagnosis of cloaca.