The cancer of the bones cells is known as osteosarcoma. In very rare cases, it occurs in soft tissues outside the bone. Osteosarcoma is most common in long bones, usually in the legs, but sometimes in the arms. It can, however, begin in every bone. Osteosarcoma tends to occur in adolescents and young adults, but may also occur in younger children and older adults. The treatment usually includes chemotherapy and surgery. Radiation therapy is generally ineffective in the treatment of osteosarcoma, although the use of new and improved radiotherapy techniques, such as proton beam therapy, is being investigated. The treatment of osteosarcoma has improved greatly over the years. Perspectives (prognosis) and treatment decisions depend on the location of the osteosarcoma, the size of the tumor, the type and extent of the osteosarcoma, and whether cancer has spread or not. After completing the treatment, patients will need a life-long follow-up to detect possible late effects of intensive chemotherapy.