Bone metastases are a major cause of morbidity for men with prostate cancer. Complications of bone metastases include pain, fractures, and spinal cord compression. Although they appear osteoblastic by radiographic imaging, most bone metastases are characterized by excess osteoclast number and activity. In addition, pathologic osteoclast activation is associated with increased risk of skeletal complications. Zoledronic acid, a potent inhibitor of osteoclast activity, differentiation, and survival, decreases the risk of skeletal complications in men with androgen-independent prostate cancer and bone metastases. Other bisphosphonates, including pamidronate and clodronate, seem to be ineffective in this setting. The reduction in risk of skeletal complications with zoledronic acid must be weighed against potential adverse effects. Additional studies are needed to determine the optimal timing, schedule, and duration of treatment in men with bone metastases as well as the potential role of bisphosphonates in other settings including the prevention of bone metastases.