Prostate cancer patients treated with LHRH agonists (e.g., leuprolide) lose bone mineral density. This is similar to post-menopausal osteoporosis. Risedronate is approved to prevent osteoporosis. We hypothesize that risedronate may also be effective in prostate cancer patients treated with LHRH agonists.

IV bisphosphonates have proven effective in treating bone loss in prostate cancer patients treated with LHRH agonists. However, it is yet to be determined if an oral bisphosphonate such as risedronate could offer the same benefits.

Inclusion Criteria:

• Patients over 18 years of age.
• Histologically confirmed diagnosis of prostate cancer without metastases.
• Patient must have negative bone scan to rule out bone metastases.
• Patient for whom androgen deprivation therapy with leuprolide acetate is indicated for at least 1 year.
• Eastern Cooperative Oncology Group (ECOG) score of 0 - 2.
• Study medication must be started within 3 months of initiation of ADT.
• Signed written informed consent.

Exclusion Criteria:

• Prior ADT (greater than 3 months).
• History of treatment with calcitriol or bisphosphonates.
• Suppressive doses of thyroxine within the previous year.
• Concomitant or prior history of long-term treatment (greater than or equal to 3 months) with systemic glucocorticoids.
• Evidence of any of the following conditions per subject self-report or chart review:

Current hyper- or hypothyroidism (stable on thyroid replacement therapy is allowed, if TSH is within normal reference range).

Paget's disease, Cushing's disease, hyperprolactinemia, chronic liver disease. Unstable systemic disease including active infection, uncontrolled hypertension, unstable angina, congestive heart failure, or myocardial infarction within 6 months before randomization.

Major surgery or significant traumatic injury occurring within 1 month prior to randomization.

• Known hypersensitivity to leuprolide acetate or any of the components found in Eligard
• Any concurrent condition that would make it undesirable, in the physician's opinion, for the subject to participate in the study or would jeopardize compliance with the protocol.