Primary osteosarcoma of the pelvic bones represents less than 10% of all osteosarcoma. Despite mutilating surgical procedures or high-dose radiotherapy and neoadjuvant chemotherapy, local failures and distant metastases remain common. The 2-year actuarial survival rate is less than 50% and the disease-free survival is under 20% at 2 years. We report 4 cases of pelvic osteosarcoma treated by a combination of chemotherapy, photon beam and neutron beam radiotherapy. After a median follow-up of 24 months, all 4 patients are alive and disease free.