Approximately 20000 men 55-67 years of age from two areas in Finland were identified from the Population Registry and randomized either to the screening arm (1/3) or the control arm (2/3) of a prostate cancer screening trial. In the first round, the participation rate in the screening arm was 69%. Of the 5053 screened participants, 428 (8.5%) had a serum prostate-specific antigen (PSA) concentration of 4.0 ng/ml or higher, and diagnostic examinations were performed on 399 of them. A total of 106 cancers were detected among them corresponding to a positive predictive value of 27%, which is comparable with mammography screening for breast cancer. The prostate cancer detection rate based on a serum PSA concentration of 4.0 ng ml(-1) or higher was 2.1%. Approximately nine out of ten screen-detected prostate cancers were localized (85% clinical stage T1-T2) and well or moderately differentiated (42% World Health Organization (WHO) grade I and 50% grade II), which suggests a higher proportion of curable cancers compared with cases detected by other means.