We report 3 cases of multifocal synchronous osteosarcoma constituting 1% of osteosarcoma cases in the Scottish Bone Tumour Registry over 30 years. All were children and had a median age of 10 years. They all presented with multiple bony lesions in the absence of demonstrable pulmonary metastases. Treatment was with palliative radiotherapy in two and combination chemotherapy and radiotherapy in the most recent case. Survival was poor in all cases, with a median of 7 months. A proposal is made for genetic studies in future cases to help elucidate the origin of these tumours. The multicentric and metastatic hypotheses are discussed.