INTRODUCTION: Approximately 30% of patients with renal cell cancer (RCC) develop bone metastasis causing skeletal-related events (SRE): pathologic fracture, spinal cord compression, surgery to bone and radiotherapy. Zoledronic acid demonstrated significant clinical benefit in RCC patients in a retrospective analysis. Primary objective of this prospective study was the proportion of patients experiencing ≥ 1 SRE during 12 months of zoledronic acid treatment and to verify the retrospective data. MATERIALS AND METHODS: Fifty patients with histologically confirmed RCC and evidence of ≥ 1 cancer-related bone lesion and ≤ 3 prior bisphosphonate applications were enrolled in 19 German centers between 2004 and 2007. The patients received 4 mg zoledronic acid every 3 weeks for 12 months followed by a follow up period for overall survival of 12 months. Bone lesions were diagnosed by bone scan or MRI-quickscan. Greater and equal to 1 lesion had to be confirmed by x-ray, CT or MRI scan. Additional bone scans were performed after completion of study treatment and if clinically indicated. In case of suspicion or evidence of a SRE it had to be confirmed radiologically. RESULTS: In total, 49 of the 50 enrolled patients were treated. Only 11 of them (22.4%) experienced any SRE until month 12. Patients with > 6 lesions and higher baseline MSKCC (Memorial Sloan-Kettering Cancer Center) score had a higher risk for SREs. Zoledronic acid was generally well tolerated and its known safety profile was affirmed. CONCLUSIONS: This prospective study confirms the results of prior data about the efficacy of zoledronic acid in patients with metastatic (m)RCC, supporting its beneficial use in these patients.