Objective: To assess the occurrence of both bladder and prostate tumours in five welldefined cancer registries.Methods: Anonymous data were provided from each cancer registry on all male bladder andprostate cancers (invasive and non-invasive). Poisson regression was used to model therate of developing the second primary tumour and generated incidence rate ratios (RRs)with 95% confidence intervals.Results: For bladder cancer and prostate cancer as first diagnosis, there was an excess riskto develop the second neoplasm. The RR decreased with increasing age of the patients. Noeffect of the initial treatment of the first neoplasm was found.Conclusion: This analysis found an excess risk to develop prostate cancer in bladder cancerpatients younger than 70 years and the first year of follow-up after the diagnosis of bladdercancer. This may be due to detection bias, although a common aetiology may also bepresent.