Inclusion Criteria:

• Histologically proven adenocarcinoma of the prostate
• Bone-scan documented metastases
• Age > 18 years
• Non-controlled bone pain despite systemic anti-tumor therapy (hormone or chemotherapy) initiated at least 4 weeks before inclusion
• Life expectancy > 3 months
• Written informed consent

Exclusion Criteria:

• New systemic anti-tumor therapy initiated less than 4 weeks before study entry or predictable need for starting a new treatment within 8 weeks
• Radiation therapy on bone target lesions or bone-targeted isotope therapy (strontium or samarium) completed less than 4 weeks before study entry
• Bisphosphonate therapy within 8 weeks before study entry
• Abnormal renal function (serum creatinine > 2 x the upper normal limit or creatinine clearance < 30 ml/min)
• Corrected serum calcium > 3 mmol/L or < 2 mmol/L
• Clinically relevant hypersensitivity to zoledronic acid, or another bisphosphonate, or one component present in the formulation of the study drug
• Severe concomitant medical condition that could hamper patient's quality of life or influence the interpretation of pain
• Patients unable to fill in a questionnaire (neurologic or psychiatric conditions, illiteracy, etc.)

Other protocol-defined exclusion criteria may apply.