Context: Bisphosphonate-related osteonecrosis (BON) of the jaws is a newly identified condition for which the exact mechanism involved in its pathogenesis remains obscure. Objective: The objective of the study was to evaluate whether diabetes mellitus (DM) may be a contributing factor in the development of BON. Design: From 2004 to 2006, 31 patients were diagnosed with BON. The diagnosis of BON was based on the medical and dental history of each patient as well as the observation of clinical signs and symptoms of this pathological process. DM was based on two consecutive fasting blood glucose levels above 7 mmol/liter. Setting: The study was completed in the Hebrew University-Hadassah Hospital referral center. Results: Of the 31 patients with BON, 18 (58%) were found to have DM or impaired fasting glucose. The proportion of diabetic patients was much higher than expected relative to the incidence of DM in the general population (14%) and compared with the proportion of diabetic patients in a control group of oncological patients treated with bisphosphonates and without BON (12%) (P = 0.00003). Conclusions: This finding indicates that DM may be a risk factor for BON and that DM patients treated with bisphosphonates should be carefully monitored. We discuss here the bone metabolic pathways characteristic of DM patients and the way in which these pathways can augment the effects of bisphosphonates.