Abstract
Extraskeletal osteosarcoma (ESOS) occurs when an osteosarcoma presents in a primary location outside of the bone. These account for only 1% of all sarcomas. We present the case of a 78-year-old male with palpable right lower quadrant mass who had ESOS in a bladder diverticulum. Less than 50 cases of ESOS in the bladder have been reported. This marks the fourth case of primary osteosarcoma found within a bladder diverticulum.