Background: Surgical margin involvement (M+) by PC at RP is associated with suboptimal bRFS; however, the interaction of M+ with coincident high-risk clinicopathologic and treatment factors obscures accurate estimation of recurrence risk. The objective of this study is to determine whether ME permits risk stratification. Methods: Retrospective analysis of clinicopathologic factor association with bRFS. Eligible patients underwent RP alone for clinically localized PC. Patients with metastatic disease, PSA > 30 at diagnosis, pathologic involvement of seminal vesicles or lymph nodes at RP, insufficient follow-up, or receipt of pre-RP or adjuvant therapy were excluded. Slides from RP specimens with close or positive margins were re-reviewed by study pathologists blinded to outcome. Results: From 2002-2010, 667 patients were eligible for analysis. The median age was 61 yrs (range, 43-76), and all had cT1-2 disease (83% T1c), with median PSA 5.6 (0.9-28.0; 85% ≤10). Robot-assisted RP was employed in 141 cases (21%). Two hundred ten patients (31%) had M+, with single maximal ME 3mm (0.1-23), and cumulative ME 4mm (0.1-34). At median follow-up of 102 months (13-184), 149 patients (22%) had recurrence, with estimated 8-year bRFS rates of 85%/56% for M-/+ patients (p < 0.01). Multivariable analysis identified PSA, Gleason score (GS), extraprostatic extension, and M+ as associated with bRFS. Specific to patients with involved margins, the combination of ME and GS permitted recurrence risk stratification, with a low-risk subset identified (GS≤6 and ME < 3mm; Table). Conclusions: The current investigation suggests that GS6 patients with maximal or cumulative ME < 3mm appear to have favorable early 8-year bRFS following RP. GS6 patients with wider ME and GS ≥7 with any extent M+ appear to have suboptimal bRFS. RP pathology reports should include ME details, in order to more precisely estimate risk of subsequent disease recurrence.