Osteonecrosis of the jaw (ONJ) is a severe bone disease (osteonecrosis) that affects the jaws (the maxilla and the mandible). Various forms of ONJ have been described over the last 160 years, and a number of causes have been suggested in the literature.

Osteonecrosis of the jaw associated with bisphosphonate therapy, which is required by some cancer treatment regimens, has been identified and defined as a pathological entity (bisphosphonate-associated osteonecrosis of the jaw) since 2003.The possible risk from lower oral doses of bisphosphonates, taken by patients to prevent or treat osteoporosis, remains uncertain.