The aim of this study was to determine the incidence of multiple bladder-prostate cancers in the population of the Italian region of Umbria and to clarify some diagnostic aspects. Prostate and bladder cancer incidence data in Umbria were obtained from cancer registry records. In the period from 1994 to 2004, 3,470 new patients with bladder cancer and 5,430 new patients with prostate cancer were registered. Among these patients there were 238 who presented multiple bladder and prostate cancers. Synchronous cancers were detected in 74 of these patients. Fifty-four of them had simultaneous tumors (diagnosed during the same hospitalization), while in 16 patients bladder cancer was detected earlier than prostate cancer and in 4 patients the opposite occurred. This study confirmed an increase in prostate cancer diagnoses in patients with bladder cancer. The increase was mainly accounted for by the detection of prostate cancers during cystectomies performed for bladder carcinoma.