Breast metastases are uncommon and typically spread from contralateral breast carcinomas. Breast metastases that spread from extramammary malignancies are even less common, and account for 0.5%-6.6% of all malignant breast disease. As extrapulmonary metastases from osteosarcoma are uncommon, breast metastasis from osteosarcoma is extremely rare. We report a case of breast and peritoneal metastases from a tibial osteosarcoma 18 months after diagnosis, and 9 months after surgery and adjuvant chemotherapy. Computed tomography findings of multiple calcified and noncalcified tumour deposits in the lungs, pleura, peritoneum, chest wall and both breasts are described.