An undesirable effect associated with bisphosphonates is osteonecrosis of the jaw (ONJ). Case reports discussed ONJ development in patients with multiple myeloma or metastatic cancers receiving bisphosphonates as palliation for malignant bone disease. No causative relationship has been unequivocally demonstrated between ONJ and bisphosphonate therapy. To determine if a higher sensitivity to bisphosphonates could in part explain the development of ONJ, the segregation of A/C rs2297480 polymorphism of gene encoding for the farnesyl pyrophosphate synthase (FDPS) with ONJ was evaluated in a cohort of 68 Caucasian patients treated with zoledronic acid for multiple myeloma and metastatic mammary and prostate cancer. The AA and CC genotypes were highly differently distributed among ONJ patients and controls, matched for sex and type of malignant disease, with a positive correlation between AA carrier status and occurrence of ONJ (p=0.03) after 18-24 months of treatment. Because FDPS gene variants have been associated with bone morbidity, these pharmacogenetic association likely reflect the interaction of amino-bisphosphonates with germline sensitivity to drug actions, and might identify patients at highest risk to develop ONJ.