BACKGROUND: Almost all patients that undergo hormonal manipulation for metastatic prostate cancer will ultimately progress because of hormone resistance. Therefore we assessed the effect of early addition of intravenous Mitomycin C to orchiectomy in patients with newly diagnosed metastatic prostate cancer. PATIENTS AND METHODS: 178 patients with histologically proven and previously untreated metastatic prostate cancer were included in a prospective, randomized multicenter trial. Randomization was done centrally between orchiectomy alone and orchiectomy with Mitomycin C. 148 patients were evaluable. RESULTS: At the final analysis 139 patients have deceased. The remaining 9 patients are still alive, but all present progression. There was no statistically significant difference in the real time to progression, or in the estimated cancer related and overall survival between both groups. Mean time to progression was 29 months in group 1 (orchiectomy alone), and 26 months in group 2 (orchiectomy and Mitomycin C) (p = 0.64). Mean time to cancer related death was 32 months and mean overall survival was 31 months in both groups. CONCLUSIONS: Mitomycin C has no beneficial effect when used in conjunction to orchiectomy in patients with newly diagnosed metastatic prostate cancer.