Prostate cancer mass screening using serum prostate-specific antigen (PSA) has been conducted widely in the world. However, little is known about the true prevalence of prostate cancer in the 'normal' PSA range (4.0 ng/mL or less). The aim of the present study was to elucidate the clinicopathological features of prostate cancer occurring in men with a wide range of PSA levels. The study comprised 349 male patients who underwent radical cystoprostatectomy for bladder cancer. Patients who had had treatment for known prostate cancer were excluded. Tissue specimens were reviewed microscopically. Ninety-one patients (26.1%) were found to have prostate cancer, and 68 (74.7%) of these 91 cancers were considered to be clinically significant. Both increasing patient age and PSA level were significantly correlated with an increased incidence of both all and significant prostate cancers. Sixty-five (21.9%) among 297 patients with PSA < 4.0 ng/mL had prostate cancer, and 45 (69.2%) of the 65 cancers were significant cancers. Eighteen patients had prostate cancers 0.5 mL or more in volume. Among the 18 patients, the PSA level was 4 ng/mL or more in 11, and 3 ng/mL or more in 15. Our study shows that prostate cancer is a common finding in radical cystoprostatectomy specimens excised because of bladder cancers, and a significant proportion of these cancers are clinically significant. PSA still appears to be a useful screening tool for detecting prostate cancers with significant volume.