Purpose: To assess the ability of magnetic resonance imaging (MRI) to diagnose extraprostatic extension (EPE) in prostate cancer. Materials and Methods: With Institutional Review Board (IRB) approval, 149 men with 170 0.5 mL tumors underwent preoperative 3T MRI followed by radical prostatectomy (RP) between 2012-2015. Two blinded radiologists (R1/R2) assessed tumors using Prostate Imaging Reporting and Data System (PI-RADS) v2, subjectively evaluated for the presence of EPE, measured tumor size, and length of capsular contact (LCC). A third blinded radiologist, using MRI-RP-maps, measured whole-lesion: apparent diffusion coefficient (ADC) mean/centile and histogram features. Comparisons were performed using chi-square, logistic regression, and receiver operator characteristic (ROC) analysis. Optimal SENS/SPEC for diagnosis of EPE were: size 15 mm 5 67.7/66.7% and LCC 11 mm 5 84.9/44.8%. 10 th -centile ADC and ADC entropy were both associated with EPE (P 5 0.02 and < 0.001), with AU-ROC 5 0.56 (0.47-0.65) and 0.76 (0.69-0.83), respectively. Optimal SENS/SPEC for diagnosis of EPE with entropy 6.99 was 63.3/75.0%. 25 th -centile ADC trended towards being significantly lower with EPE (P 5 0.06) with no difference in other ADC metrics (P 5 0.25-0.88). Size, LCC, and ADC entropy improved sensitivity but reduced specificity compared with subjective analysis with no difference in overall accuracy (P 5 0.38). Conclusion: Measurements of tumor size, capsular contact, and ADC entropy improve sensitivity but reduce specificity for diagnosis of EPE compared to subjective assessment. Level of Evidence: 3 Technical Efficacy: Stage 2