Purpose: To investigate the relationship between lesion size determined using mpMRI and histopathological findings of specimens obtained after mpMRI fusion biopsy and radical prostatectomy. Material and Methods: We retrospectively analyzed 590 patients with PCa who underwent an MRI fusion biopsy between 2017-2019. We measured the diameter of suspicious tumor lesions on diffusion-weighted mpMRI and stratified the cohort into two groups. Group A included patients with a suspicious tumor lesion equal and smaller than 10 mm and Group B included those with a suspicious tumor lesion larger than 10 mm. RP was performed in 53 patients. The patients in Groups A and B were compared according to their pathological findings obtained with fusion biopsy and RP. Results: After applying the inclusion and exclusion criteria, Group A consisted of 144 patients and Group B comprised 146. In Group B, PI-RADS score determined in mpMRI was higher than Group A, and there was a statistically significant difference between the two groups in terms of clinical T-stage. The PCa detection rate and the number of positive cores were statistically significantly higher in Group B than in Group A. In addition, there was a statistically significant difference between the two groups in relation to the biopsy, the ISUP grades and the presence of clinically significant PCa. In Group B, pathological T-stage and extraprostatic extension (EPE) and surgical margin (SM) positivity were found to be higher among the patients who underwent RP. In the multivariate analysis, the mpMRI lesion size being >10 mm was found to be an independent predictive factor for SM and EPE positivity. Conclusion: The radiologists and clinicians should be awared of the possibility of presence of features that may affect local staging, such as EPE positivity, in the presence of lesions larger than 10 mm in which prostate cancer is detected.