A 6 mo old 13.5 kg (29.7 lb) male intact American Staffordshire terrier was evaluated for a history of supernumerary pelvic limbs, with malodorous discharge from a supernumerary penis. Imaging (radiographs, abdominal ultrasound, and computed tomography with excretory urogram) showed a supernumerary pelvis with associated pelvic limbs, no osseous continuity with the primary spinal column, a colonic diverticulum extending to the supernumerary pelvis, an enlarged left kidney with a ureter connecting to a single bladder, right renal aplasia, a single descended testicle in the primary scrotum, an intra-abdominal cryptorchid testicle, and two unidentifiable soft tissue masses. At surgery, a single ileum was present with a primary and accessory cecum and colon and the accessory colon entering the supernumerary pelvis. The accessory cecum and colon, right kidney, two unknown soft tissue masses, and the single descended testicle were removed. The right kidney had a ureter that anastomosed with the accessory colon at its entry into the supernumerary pelvis. The supernumerary pelvis and hind limbs were not removed. Five months after surgery, the dog was reported to be doing well clinically. Caudal duplication is extremely rare in veterinary medicine. The appearance of supernumerary external structures may indicate internal connections as well.