Objective: To compare the diagnostic performance for the detection of clinically significant prostate cancers and interobserver agreement between PI-RADS v2 and v2.1 Material and Method: The mpMRI images of 258 patients and 394 nodüles included in this retrospective study were obtained on 3T MR and evaluated by two radiologists according to PI-RADS v2 and v2.1. Sensitivity and specificity between v2 and v2.1 were compared. Detection rates for clinically significant prostate cancers were evaluated. Interobserver agreement was evaluated using κ statistics. Results: PI-RADS v2.1 and v2 had higher sensitivity and lower specificity (100%, 52.38%) in the peripheral zone, and showed higher sensitivity and specificity (92.86%, 98.79%) in the transition zone for category ≥4 lesions to estimate csPCa, but no remarkable difference was found between the two versions. Interobserver agreement was statistically significant and very weak in the transition zone (κ=0.383, κ=0.279, respectively), very strong in the peripheral zone (κ=0.869) according to both classifications and they were similar. Conclusion: The diagnostic performance of PI-RADS v2 and v2.1 were found similar in the determination of clinically significant cancers and all cancers in both zones. The clinically significant cancer detection rate in category 2+1 lesions in the transition zone was higher than in category 2 lesions but it was not statistically significant. Interobserver agreement was low in the transition zone and very strong in the peripheral zone in both versions.