Inclusion Criteria:

• Signed informed consent
• Age > 18 years
• Histologically confirmed diagnosis of carcinoma of the prostate
• ECOG performance status of 0, 1, or 2
• No radiological evident bone metastasis (negative bone scan or verification of suspected foci as benign lesions by additional radiological examination)
• T3-4 AND highest pre-study PSA >20 ng/ml AND Gleason score = 8 (or Gleason grade = 4)
• Patients with prior prostatectomy or prior local radiotherapy are eligible for this study
• Patients are destined to receive medical (LHRH analogue) or surgical (orchiectomy) castration and Zometa® treatment will start not later than 6 weeks after surgery
• Patients should be fully recovered from prior interventions where applicable

Exclusion Criteria:

• Patients with a serum creatinine determination >265 µmol/L (3.0 mg/dL)
• Patients that received prior medical (LHRH analogue) castration
• Current (or previous) evidence of metastatic disease to the bone
• History of any other neoplasm within the past five years except for nonmelanomatous skin cancer.
• Previous hormonal therapy with LHRH agonists or other forms of hormonal ablation
• WBC<3.0x109, ANC < 1500/mm3, Hgb<8.0 g/dL, platelets < 75 x 109/L
• Liver function tests >2.5 ULN
• Prior treatment with Zometa® (zoledronic acid) or other bisphosphonates
• Treatment with calcitonin, mithramycin, or gallium nitrate within 2 weeks prior to the date of randomization (Visit 2)
• Use of other investigational drugs (drugs not marketed for any indication) within 30 days prior to the date of randomization (Visit 2)
• Patients with evidence in the six months prior to randomization of severe cardiovascular disease (defined as uncontrolled congestive heart failure), hypertension refractory to treatment, or symptomatic coronary artery disease uncontrolled by treatment
• History of noncompliance to medical regimens and patients who are considered potentially unreliable or incapable of giving informed consent as judged by the investigator.