An open, multicenter and prospective study to evaluate the impact of the treatment with zoledronic acid 4 mg, on the quality of life and the skeletal-related events in patients with prostate cancer and bone metastasis that responds to hormonal therapy. Zoledronic acid is given to patients in a 15 minute-infusion every 4 weeks until a skeletal-related event occurs.

Inclusion Criteria:

• Age ≥18
• histologically confirmed adenocarcinoma of the prostate.
• Orchidectomy within the four previous weeks to enter the study.
• bone metastasis evidenced by bone scan.
• A hip DEXA study with a DS < 3.
• No hormonal therapy previous to enter the study.
• ECOG performance score of 0-2.
• Signed written informed consent.

Exclusion Criteria:

• Abnormal renal function evidenced by a creatinine clearance ≤60 ml/min.
• Any kind of hormonal therapy for prostate cancer previous to enter the study.
• Serum calcium corrected for albumin level < 8.0 mg/dl.
• WBC < 3.0x10^3, ANC < 1500/mm3, Hemoglobin < 8.0 g/dl, platelets < 75 x 10^3/l.
• Abnormal hepatic function evidenced by ALT and AST value >2.5 UNL
• Subjects with any other malignant disease that can affect the bone.
• Subjects with any other non malignant disease that can jeopardize the evaluation of the primary objectives of this trial (severe osteoporosis) or that do not aloud perform the trial evaluations.
• Known hypersensibility to zoledronic acid or other bisphosphonates.
• Subjects that in the investigator's opinion can not cooperate with the protocol.

Other protocol inclusion/exclusion criteria may apply.