Background: Osteonecrosis of the jaw (ONJ) is a destructive bone process in patients undergoing bisphosphonate therapy and it is modulated by local and systemic factors. The purpose of this article is to determine the prevalence of ONJ in patients who have undergone intravenous bisphosphonate therapy, and relate the risk factors described to establish a protocol to reduce the risk of developing ONJ. Material and Methods: We performed a retrospective study on 194 patients treated with IV bisphosponates, analyzing clinical and pathological variables. Results: The prevalence of ONJ was 12.9 %. The most remarkable complication was pain, which was reported by 80% of patients. The average age of the patients undergoing bisphosphonate therapy was 68.91 years. Most of non-diabetic patients did not develop ONJ (92.3%) ( p =0.048). During bisphosphonate therapy, 3.1% of patients underwent extractions in the same percentage in the maxilla and in the mandible; all of which, except for one patient, developed ONJ ( p <0.001). In regards to the periodontal state, 94.3% of patients without periodontal problems did not develop ONJ ( p =0.001). Almost 50% of the necrosis were located unifocally on the mandible ( p <0.001). The number of affected patients and the aggressiveness of the disease increased significantly three years after starting treatment ( p <0.001). Conclusions: Etiology still is a controversial issue and we should focus on known risk factors, such as the development of surgical procedures in patients undergoing bisphosphonate therapy, especially in patients who have already started their treatment, a group in which ONJ prevalence increases. Moreover, a bad periodontal state in these patients is also an important risk factor, and the control of diabetes reduces it. Due to the above, all patients should be diagnosed and educated in oral hygiene prior to treatment, performing periodical maintenance, to detect possible traumatisms and periodontal infection as soon as possible.