The authors report a case of peritoneal and chest wall metastases in a 17-year-old boy previously diagnosed of femur osteosarcoma with metastases in the lung and bones. Although the patient achieved complete remission after initial treatment, he presented with lung metastasis 15 months after initial diagnosis. They were resected 3 times and he received second-line chemotherapy with gemcitabine and docetaxel. However, 31 months after initial diagnosis he presented with abdominal and chest wall masses. In this report the authors discuss clinical outcomes and how unusual sites of metastasis are being increasingly reported after the use of new treatments.