Objective: To compare oncological outcomes for segmental vs main renal vein invasion (RVI) in patients with renal cell carcinoma (RCC). Patients Methods: Patients undergoing extirpative surgery for RCC at our institution between 2003 and 2013 were stratified into five groups according to clinical stage: T2 (n = 135), T3a with fat invasion (n = 185), T3a with segmental RVI (n = 87), T3a with main RVI (n = 64) and T3b (n = 40). Kaplan–Meier survival analysis and multivariable Cox regression were performed to determine the impact of segmental RVI on recurrence-free survival (RFS) and cancer-specific survival (CSS). Harrell's c index was used to compare the prognostic accuracy of current and proposed staging models. Results: At a median follow-up of 37 months, both RFS and CSS were significantly worse for patients with main RVI as compared with segmental RVI (P = 0.03 and P = 0.009, respectively). On multivariable analysis, main RVI had inferior RFS (hazard ratio [HR] 2.3, 95% confidence interval [CI] 1.1–4.4; P = 0.03] and CSS (HR 3.5, 95% CI 1.3–9.9; P = 0.02) compared with segmental RVI. Sub-stratifying T3a disease by separating segmental and main RVI improved prognostic accuracy compared with the current staging system for CSS (c indices 0.66 vs 0.59) and RFS (0.70 vs 0.60). Conclusions: Main RVI is independently associated with worse RFS and CSS than segmental RVI. These findings may have significance for patient counselling and future staging guidelines.