INTRODUCTION: Approximately 85% of patients who die from prostate cancer present the spread of bone metastases. Even though the radiological appearance of such metastases is osteoblastic, it is now known that these lesions coexist in their microenvironment with blastic and lytic lesions. The process always begins with bone lysis by osteoclast proliferation, paralleling nearby bone deposition. The treatment options are palliative and have poor clinical response with short-lived improvement. We have studied the clinical effect of bisphosphonates (clodronate) in the treatment of skeletal complications from prostate cancer. MATERIALS AND METHODS: In an open prospective study, 58 patients with hormone-refractory prostate cancer with bone metastases were assessed from November 2000 to September 2003. The mean age was 70.3 y (range: 51-87 y). Bone scintigraphy, plain X-ray, assaying of prostate-specific antigen (PSA) and biochemical tests were requested before and following treatment. Patients were previously and subsequently assessed using the visual pain scale (0-10) and Karnofsky's index after the first and second intravenous (i.v.) infusions (administration of i.v. clodronate every 28 days) and every 4-6 months thereafter. Student's t-test was used for statistical analysis. RESULTS: A total of 53 patients (91.4%) showed improvement after the first and/or second cycle, which persisted for at least 4 months (average 6.3 months). The averages on the visual pain scale improved from 7.4 (range: 2-8) to 2.4 (0-7) and on Karnofsky's index from 43 (32-58) to 73 (50-82). The radiological appearance of the metastases improved in 27 patients (46.5%) and there were few relapses (six patients; 10.3%). CONCLUSIONS: Clodronate was effective in the treatment of skeletal complications from prostate cancer. There was an objective response in 91.4% of treated patients, with a marked improvement in the subjective visual pain scale evaluation as well as on Karnofsky's index, with low side effects.