Background:The prediction of positive surgical margins (SM) after radical prostatectomy (RP) is important for planning the surgical modality and adjuvant therapy in patients with prostate cancer (PCa).Objectives:To investigate factors affecting SM positivity in patients diagnosed with PCa who underwent RP using the PCa database of the Urooncology Association (Turkey).Methods:Patients who underwent RP due to clinically T1c-T3 PCa and who had detailed SM data for the RP specimen were included in the study. Pathological data of 12 core transrectal ultrasound prostate biopsies and RP were evaluated. Patients were divided into 2 groups (SM positive and SM negative) according to SM status after RP. Data were compared between the groups. Factors affecting SM positivity, the number of positive SM sites, and the location of positive SM were separately evaluated with regression models.Results:A total of 2,643 patients from 6 different centers (median age: 63 years) with a prostate-specific antigen (PSA) level of 7.3 ng/mL were investigated in the study. BMI, PSA, biopsy Gleason score (GS), and perineural invasion (PNI) were found to be independent predictive factors for SM positivity and the number of positive SM locations, respectively (p< 0.05). According to the positive SM location, PSA was found to be associated with positive SM in apex, anterior prostate, and bladder neck locations. Also, according to posterolateral SM status, PNI and nerve-sparing RP (nsRP) rates were 21.3 and 44% for patients with negative posterolateral SM, and rates were 35.4 and 50.6% for patients with positive posterolateral SM, respectively (p< 0.05). In patients who underwent nsRP, positive SM was present in 22.2% of patients who did not have PNI on prostate biopsy, whereas positive SM was present in 40.6% of patients with PNI (p< 0.001). Similarly, 10.9% of patients without PNI had positive posterolateral SM, whereas 17.3% of patients with PNI had positive posterolateral SM (p= 0.031).Conclusions:BMI, PSA, biopsy GS, and biopsy PNI positivity were found to be predictive factors affecting SM positivity. The most important factors affecting posterolateral positive SM were biopsy PNI and nsRP, indicating that the nsRP approach may cause positive SM in the posterolateral margin of the prostate (neurovascular bundle location) in patients with positive PNI on biopsy.