Multifactorial analysis of patients with osteosarcoma of the distal femur and proximal tibia, recorded in the Swedish Cancer Registry during 1958 through 1968, disclosed a 5-year survival of 15.1% for femoral osteosarcomas and 38.1% for tibial tumours. The prognosis was better in adults than in children and better in males than in females. Tumour size, soft tissue involvement, the presence of pathological fracture and the duration of symptoms before treatment influenced the prognosis. The best treatment for the tibial lesions was high amputation alone, whilst for the femoral tumours primary ablative surgery was not superior to combined high-dose radiotherapy and delayed amputation. The main cause for the higher survival rate for tibial neoplasms seemed to be the fact that they were less advanced on admission than those of the distal femur. The findings emphasize the importance of early diagnosis and treatment for improved survival.