The purpose of this study is to see if giving zoledronic acid three times a year is as effective as five times a year, in increasing bone strength in men with prostate cancer. All participants will receive the active drug but half will receive drug every 6 months and the other half will receive drug every 3 months. Both patient and doctor will know which treatment a patient is receiving.

After 1 year of treatment bone strength will be measured with scans and compared to the strength at the start of the study. All participants will stop receiving the drug after 1 year and will be seen back in the clinic, annually for another 2 years for follow-up.

Inclusion criteria:

Histologically confirmed diagnosis of carcinoma of the prostate

• No distant metastases
• Patients must be candidates for androgen deprivation therapy (ADT)
• Patient with a baseline BMD T-score at or below -1 standard deviations in the lumbar spine (L2-L4) are eligible

Exclusion criteria:

Patients with normal BMD at trial entry

• Patients who received any prior bisphosphonate therapy in the past 12 months
• Treatment with anti-androgen mono- or combination therapy
• Patients who are currently receiving diethylstilbesterol (DES) or who have previously received PC-SPES
• Patients who have received prior treatment with systemic corticosteroids within the past 12 months
• Patients with prior exposure to anabolic steroids or growth hormone within the past 6 months
• Patients with any prior treatment for osteoporosis

Other protocol-defined inclusion/exclusion criteria may apply.