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

Inclusion Criteria

• Patients aged ≥18 years
• Written informed consent
• Histologically-proven prostate carcinoma
• ECOG performance status ≤ 2
• Life expectancy > 6 months
• Newly diagnosed (≤ 6 months prior to visit 1) bone metastases evidenced by bone scan or radiograph.
• Patients on androgen deprivation therapy (medical therapy with LHRH analogues + antiandrogens or surgical castration) or going to start it
• Patients with partners of childbearing potential should use a barrier method of contraception throughout the study

Exclusion Criteria

• Patients without a history of metastatic disease to the bone
• Prior treatment with bisphosphonates
• SREs prior to visit 2
• Prior treatment with calcitonin, mithramycin, or gallium nitrate within 2 weeks prior to baseline
• Corrected (adjusted for serum albumin - see Appendix 5 for the calculation) serum calcium concentration < 8.0 mg/dl (2.00 mmol/l)
• Serum creatinine concentration > 265 micromol/l (3.0 mg/dl) or a calculated creatinine clearance < 30 ml/minute or serious underlying renal disease or prior renal transplantation
• History of other malignant neoplasm within previous five years with exception of non-melanomatous skin cancer which has been satisfactorily treated
• Other known concurrent, severe medical disorder jeopardizing the life of the patient in the immediate future
• Patients treated with systemic investigational drug(s) and/or device(s) within the past 30 days or topical investigational drugs within the past 7 days
• Known hypersensitivity to zoledronic acid or other bisphosphonates
• History of noncompliance to medical regimens and patients who are considered potentially unreliable (for example drug or alchohol abusers) or incapable of giving informed consent as judged by the investigator