Osteonecrosis of the jaw (ONJ) was first reported in the dental literature in 2003. The term was coined to describe a spectrum of dental problems seen in cancer patients treated with high doses of intravenous bisphosphonates for the prevention of skeletal-related events. By consensus, the syndrome is now defined by the presence of exposed bone in the mouth which fails to heal after appropriate intervention over a period of 6 or 8 weeks. It is most common in patients with breast or prostate cancers, or multiple myeloma treated with bisphosphonates, of whom about 5% develop the condition. In patients receiving the much lower drug doses used in osteoporosis, the incidence appears to be ∼1/100,000 patient-years, probably comparable to that in the general population. It is likely that ONJ results from direct drug toxicity to cells of bone and soft tissue. The bone in ONJ lesions does not appear to be ‘frozen’ but rather there is very active bone resorption taking place, which is likely to be responsible for the local release at high concentrations of bisphosphonates. Infection probably plays a pivotal role in driving this resorption, so its active management is critical. Obvious abnormalities are apparent with a variety of radiologic modalities, and it is not clear that radiographs are inferior to other approaches. Most authors favor a conservative approach to surgical debridement of the lesions.