Purpose We determined the impact of increasing the number of cores from 12 to 20 at initial prostate biopsy in men suspicious of prostate cancer. Materials and Methods From December 2009 to November 2011, patients in 7 centers scheduled for a first prostate biopsy, with a prostate specific antigen less than 20 ng/ml and no nodule on digital rectal examination, were invited to participate in this superiority trial. Patients were randomized to a 12-core (PB12 group) or a 20-core (PB20 group) protocol. The primary end point was cancer detection rate. Secondary end points were cancer characteristics, rate of complications and patient tolerance assessed by a self-completed booklet before prostate biopsy and at day 5 and day 15. Results A total of 339 patients were randomized. Preoperative variables were similar in both groups. Cancer was detected in 71 patients (42.0%) in PB12 group and in 81 patients (48.8%) in PB20 group, and the difference was not significant (p >0.2). Gleason score and cancer length measured on prostate biopsy cores were not significantly different between groups. Although the cancer detection rate was linked to prostate volume, this was not affected by the number of extracted cores (p >0.4). Complications number and seriousness were comparable in both arms. No significant difference was noted regarding side effects and tolerance as self-assessed by the patient at day 5 and day 15 after prostate biopsy. Conclusions Our findings suggest that there is no significant advantage in using a 20-core biopsy protocol vs 12-core protocol during an initial prostate biopsy.