Extra-skeletal osteosarcoma (ESOS) is a rare neoplasm that represents less than 2% of all soft tissue sarcomas. Common reported sites of involvement include limbs, retroperitoneum, chest wall and buttocks. ESOS arising primarily in parenchymatous organs are extremely uncommon, with the involvement of the urinary bladder is even rarer. We herein report a case of primary ESOS of the urinary bladder in a 48 year-old male patient.