Over a period of 28 months, we observed five cases of osteonecrosis of the jaw (ONJ) in cancer patients treated with bisphosphonates (BP) at our institution. This prompted us to undertake a retrospective, multicenter study to analyse the characteristics of patients who exhibited ONJ and to define the frequency of ONJ in multiple myeloma (MM). We identified 35 cases in Gruppo Italiano Studio Linfomi centers during the period 2002 - 05. The median time from cancer diagnosis to the clinical onset of ONJ was 70 months. In these 35 cases of ONJ, 24 appeared 20 - 60 months after starting BP treatment. The time for the onset of ONJ was significantly shorter for patients treated with zoledronic acid alone than for those treated with pamidronate followed by zoledronic acid. The frequency of ONJ in the MM group during the study period was 1.9%, although the nature of the present study may have resulted in an underestimation of ONJ cases. Our analysis strongly suggested an association between the use of BP and the occurrence of ONJ, although we were unable to identify any definite risk factors with a retrospective study. The most frequently ONJ-associated clinical characteristics were chemotherapy treatment, steroid treatment, advanced age, female sex, anemia, parodonthopaties/dental procedures and thalidomide (in the case of MM patients).