A prospective study was performed in 80 patients receiving bisphosphonates in order to determine frequency of occurrence, risk factors, clinical presentation, radiology, pathology and proper treatment of osteonecrosis of the jaw (ONJ). Of 80 patients, 22 (28%) developed ONJ. There were 11 male and 11 female patients. Median age was 65 years. Ten patients (46%) had multiple myeloma (MM), 5 (23%) had breast cancer and 7 (32%) had other malignancies. Of 22 patients with ONJ, 14 patients (64%) received zoledronate, 3 (14%) received pamidronate, 4 (18%) received pamidronate later followed by zoledronate and 1 patient received ibandronate later followed by zoledronate. The median time of exposure in ONJ group was 32 months compared with 27 months in patients without ONJ. The mean induction time until bone exposure was 26 months for patients who received zoledronate, 54 months for pamidronate and 48 months for pamidronate followed by zoledronate. Thirteen patients (59%) had ONJ with bone exposure of mandible, 6 (27%) of maxilla and 3 (14%) of both jaws. ONJ occurred spontaneously in 5 patients (23%) and in 17 patients (77%) occurred after tooth extractions and surgical tooth removals (P<0.001). Nine patients (41%) had previous extractions of molars, 6 (27%) of premolars and 2 (9%) of front teeth. The cumulative hazard is significantly higher in zoledronate group (P=0.015). It was 3.48 times higher than the other group (pamidronate alone; pamidronate followed by zoledronate; ibandronate alone; etidronate alone; ibandronate followed by pamidronate; ibandronate followed by zoledronate; ibandronate followed by pamidronate and zoledronate). There was no association of ONJ with age, sex, use of high-dose or conventional chemotherapy or the use of corticosteroids, thalidomide or bortezomib (P>0.05). Patients diagnosed with multiple myeloma and breast cancer were found significantly associated with ONJ (P=0.001 and P=0.014, respectively). Long-term use of bisphosphonates (>2.5 years) increases the risk for development of ONJ. Intravenous application of zoledronate and previous dental extractions or surgical tooth removals are important risk factors of ONJ. Neither treatment with high-dose chemotherapy with autologous stem cell transplantation nor treatment with corticosteroids, thalidomide or bortezomib is a risk factor in this study.