PURPOSE: We investigated the detection rate of prostate cancer in Korean men through a population based mass screening test. MATERIALS AND METHODS: In June 2007 serum prostate specific antigen was examined in 3,943 residents in the Gangneung (1,429), Daegu (1,396) and Jeonju (1,118) areas who were 55 years or older with prostate specific antigen 3.0 ng/ml or greater considered the criterion for 12-site transrectal biopsy recommendation. The serum prostate specific antigen distribution and the cancer detection rate were analyzed according to participant regions and age groups. RESULTS: Mean +/- SD serum prostate specific antigen in the entire cohort was 2.4 +/- 8.6 ng/ml. It significantly increased with increasing age, that is 1.2, 2.2, 3.4 and 4.7 ng/ml in the groups 55 to 64, 65 to 74, 75 to 84 and 85 years or older, respectively (p <0.0001). However, no regional differences were noted among Gangneung, Daegu and Jeonju (2.2, 2.7 and 2.3 ng/ml, respectively, p = 0.290). Biopsy candidates represented 7.3% (48 men), 17.7% (395), 25.5% (240) and 32.7% (36) of the 55 to 64, 65 to 74, 75 to 84 and 85 years or older groups, respectively, or 18.2% of the entire cohort of 719. Of biopsy candidates 268 (37.3%) had undergone biopsy, of whom cancer was detected in 76 (28.4%) for a cancer detection rate and estimated cancer detection rate of 1.93% and 5.17%, respectively. The age adjusted estimated cancer detection rate (55 years or older) was 3.36%. Cancer detection increased significantly with increasing prostate specific antigen, that is 12.3% at 3.0 to 4.0 ng/ml, 27.3% at 4.1 to 10.0 and 64.1% at greater than 10.0. The Gleason score was 2-6 in 41 men (53.9%), 7 in 14 (18.4%) and 8-10 in 21 (27.6%). CONCLUSIONS: The estimated cancer detection rate in Korean men 55 years or older was 3.36%. The significance of the high rate in this population should be determined through repeat screening and further surveillance in the future.