The present study will give information about the course over time in skeletal-related events (SRE) in prostate cancer patients with bone metastases treated with zoledronic acid 4 mg administered as a 15-minute infusion every 4 weeks for a maximum of 15 infusions. The protocol will enroll patients with recent diagnosis of bone metastases from prostate cancer who are hormone-refractory, hormone-naïve or still hormone-sensitive, that represent the entire population of prostate cancer patients