Several studies suggest that standard 6 core sextant transrectal ultrasound (TRUS) guided biopsies of the prostate provides insufficient material to adequately detect clinically important prostate cancer, and that a larger biopsy cores may improve the cancer detection rate. We performed a prospective randomized trial by comparing 6 and 12 core prostate biopsies to determine whether doubling the number of cores in a sextant biopsy improves the prostate cancer detection rate. We randomized 240 men with an elevated serum total prostate specific antigen (PSA) level, abnormal digital rectal examination (DRE) and/or TRUS suspicious for prostate cancer into a 6 core biopsy group and 12 core biopsy group from Jan. 2002 to Jan. 2003. We acquired 3 cores from the right and left prostate lobes for the 6 core biopsy group and three additional cores from each side more peripheral than a 6 core for the 12 core biopsy group. The 6 core and 12 core biopsy groups were well matched with no significant differences in age, prostate volume, PSA and PSA density. The overall cancer detection rate by prostate biopsy was 15.8% (38/240) and the cancer detection rate was not significantly different between the 6 core biopsy group (14.4%, 17/118) and 12 core biopsy group (17.2%, 21/122) (p=0.60). Our study demonstrates no statistically significant improvement in prostate cancer detection rate by increasing the number of biopsy cores. In conclusion, we believe that the standard 6 core sextant biopsy of the prostate is as effective at detecting prostate cancer as a 12 core biopsy in Korean men.