Primary osteosarcoma of the bladder is an extremely rare type of tumour, and less than 30 adequately documented cases have been registered. From a clinical and radiological point of view, it is impossible to distinguish from other types of bladder tumours, since despite the fact that calcification of the bladder wall is common in osteosarcoma, other bladder diseases exist which may also present calcification. Prior to primary bladder osteosarcoma diagnosis, it is vital to first rule out the existence of an skeletal origin. Differential diagnosis must be carried out essentially with other bone-forming tumours, such as carcinosarcoma and transitional cell carcinoma with bone metaplasia. Prognosis for bladder osteosarcoma is extremely pessimistic, as the majority of patients do not survive beyond 6 months, regardless of the treatment carried out. We present a case of bladder osteosarcoma treated by right hemi-cystectomy, which remains disease free after a follow-up period of one year.