Background: Epidemiologic data suggests a link between obesity and increased risk of aggressive prostate cancer (PCa). Therefore, the accurate detection of prostate cancer is paramount in obese men. We sought to characterize the PCa lesions seen on multiparametric magnetic resonance imaging (mpMRI) in both obese (OB) and non-obese (nOB) patients. In addition, we examined whether obesity affects the accuracy of fusion biopsy (FBx) versus systematic biopsy (SBx). Methods: Data from patients who underwent FBx, SBx, or both, and subsequent prostatectomy at a single institution between 2007-2017 were reviewed. Men were stratified into three groups based on body mass index (BMI): normal weight (18.5-24.9), overweight (25.0-29.9), and obese (≥30.0). mpMRIs were analyzed to determine prostate size, lesion size, lesion location, and evidence of ≥T3 disease. FBx and SBx were compared to prostatectomy specimens. These variables were then analyzed between the OB and nOB groups. Results: 487 patients were included: 109 (19%) normal weight, 266 (48%) overweight, and 185 (33%) obese. No statistical differences were noted in age, PSA, or clinical stage. mpMRI showed similar prostate size, index and total lesion diameter, lesion location, and Prostate Imaging Reporting and Data System (PIRADS) score between BMI categories. In OB patients, FBx was better able to predict final Gleason score (GS) than SBx, 60% vs 47%, p = 0.0474, OR 1.67 (1.00-2.80). The rate of upgrading after SBx was higher for OB men versus nOB men, 44% vs 34%, p = 0.034, OR 1.52 (1.01-2.29). However, risk of upgrading returned to that of nOB men with FBx, 20% vs 17%, p = 0.538, OR 1.21 (0.658-2.23). Conclusions: FBx is a more accurate measure of the true GS in OB patients than SBx, and there is a significantly greater risk of underrepresenting PCa on SBx in OB patients. These findings were not associated with differences in prostate sizes and lesion characteristics on mpMRI. This suggests that obesity may cause technical challenges with prostate biopsies that may be overcome by improved visualization and targeting of FBx.