Necrosis of jaw bone as a late effect of ionizing radiation, which is used in treatment of malignancies of head and neck. It causes vascular changes with reduction in blood flow resulting in hypovascularity, hypocellularity, and hypoxia. Spontaneous necrosis of jaw bone may appear with subsequent ischemic necrosis of the covering mucous membrane and exposure of the necrotic bone to the oral cavity with a secondary invasion of the necrotic bone with microorganisms. Called also radiation‐damaged bone and soft tissues.