Osteoradionecrosis (ORN) is not exceptional, despite advances in irradiation techniques. Six cases are reported, involving the pelvis, coxofemoral joint, mandible and vertebrae; in this last case, the semiologic value of the lucent intrasomatic image seen on plain films and tomographies of the vertebrae is underscored. The irradiation dose (above 3 000 rad) is the chief factor in osteoradionecrosis, which may be precipitated by adjuvant factors and potentiating events such as trauma and infection. Pathologic study shows several lesions whose association is suggestive: cell lesions, osteoporosis, vascular lesions, and foci of necrosis. The pathogenic significance of lesions of bone cells is demonstrated, while the part played by vascular lesions is controversial. Involvement of the pelvis and hips following irradiation of pelvic carcinoma is the most common. The scapular girdle and ribs may be involved in irradiation for breast cancer. In involvement of the mandible, remarkable features are its frequency following irradiation of carcinoma of the mouth, the significant part played by potentiating factors, i.e. infection and trauma, severity of complications, i.e. fistulae and hemorrhage, and lastly difficulties of management. Among infrequent sites, involvement of the vertebrae is of interest as it may mimic collapse due to osteoporosis or metastasis. Diagnosis rests on an association of criteria, and fortunately bone biopsy is usually unnecessary. The clinical features, topographical characteristics and course of the disease allow differentiation from bone metastasis; it may be more difficult to distinguish postirradiation sarcoma, which is exceptional, or a number of benign conditions, such as aseptic necrosis, infectious osteoarthritis, and destructive coxarthrosis.