Bisphosphonates (BPs) are used to inhibit bone resorption. Recently, they have been used in cancer patients to prevent bone loss due to bone metastasis. Fourteen consecutive patients, undergoing BPs monthly IV infusion due to neoplastic bone diseases, were diagnosed with osteonecrosis of the jaws. None of the patients had been previously undergoing radiotherapy of the head and neck region. Eight patients showed maxillary involvement, and nine patients had had a recent tooth extraction in the osteonecrosis areas. Biopsies and surgical debridment were performed. Histologically, none of the patients showed signs of bone metastasis. As high-dosage long-term BP therapy appears to be associated with osteonecrosis of the jaws, dental practitioners should exercise caution in the treatment of such patients.