Radical cystoprostatectomy (RCP) followed by bilateral pelvic lymphadenectomy and urinary diversion remains the gold-standard therapy for men with localized muscle-invasive bladder cancer (MIBC). Prostate cancer might be incidentally detected at the time of RCP with a reported prevalence of 24-51%. Typically, these patients are considered to have clinically insignificant disease, but data from emerging series challenge this assumption and suggest that some of these tumours might be aggressive, or somehow increase the aggressiveness of the associated MIBC, and can negatively influence the patient's overall survival outcomes. Furthermore, the potential use of prostate-sparing cystectomy in patients with less-aggressive MIBC might lead to newly diagnosed incidental cases of prostate cancer, with characteristics suggestive of clinically significant disease, requiring a specific, separate workup. The development of evidence-based, validated protocols to define the necessary steps for diagnosis of prostate cancer in these patients, including the role of serum PSA testing, digital rectal examination, the role of imaging methods and the indication and type of biopsy protocol, is of major importance to the multidisciplinary management of patients with urological cancer. Finally, the retrospective nature of the available data account for much of the variability in the prevalence of coexisting bladder and prostate cancer and emphasizes the need for randomized trials in this controversial area of urological oncology.