Osteosarcoma probably arises from a primitive, undifferentiated mesenchyme, It is highly malignant bone tumor characterized by the invariable formation of neoplastic osteoid and tumor tissue with poor prognosis. Osteosarcoma may involve any bone, but usually arises in the metaphyseal portion of long bones, most frequently at the distal ent of the femur, the proximal end of the tibia, and the proximal end of the humerus. The authors have experienced one case (52 year old male) of osteosarcoma originating from the right patella.