Background: Postoperative complications (POCs) are associated with worse oncologic outcomes in several cancer types. The implications of complications after rectal cancer surgery are not known. Methods: The US Rectal Cancer Consortium (2007-17) was reviewed for patients with primary rectal adenocarcinoma who underwent R0/R1 low anterior resection (LAR) or abdominoperineal resection (APR). 90-day POCs were categorized as major vs minor and grouped into infectious, cardiopulmonary (CP), thromboembolic (TE), renal, or intestinal dysmotility. Primary outcomes were 5-yr overall survival (OS) and recurrence-free survival (RFS). Results: Of 1136 pts, median age was 59 yrs (IQR 51-67), 61% were male (n = 693), median f/u was 31 mos (IQR 13-54). 70% underwent LAR (n = 799) and 30% APR (n = 337). Complication rate was 46% (n = 527), with 63% minor (n = 330) and 32% major (n = 170). Of all POCs, infectious complications comprised 20% (n = 105), cardiopulmonary 3% (n = 14), thromboembolic 5% (n = 25), renal 9% (n = 46) and intestinal dysmotility 19% (n = 100). When compared to minor or no POCs, major POCs were associated with both worse RFS (48 vs 63 vs 76% p < 0.01) and OS (64 vs 76 vs 80% p < 0.01). While a single POC was associated with worse RFS (61 vs 76% p < 0.01), multiple POCs were associated with worse OS (62% vs 79% p = 0.02). Regardless of complication grade, infectious POCs were associated with worse RFS (56 vs 76% p < 0.01) while CP and TE POCs were associated with worse OS (CP 40 vs 78% p < 0.01; TE 63 vs 78% p < 0.01). Postoperative renal dysfunction was associated with both worse RFS (26 vs 76%, p < 0.001) and OS (62 vs 78% p = 0.01). This persisted on MV analysis for OS when accounting for pathologic stage, receipt of neoadjuvant therapy, and final margin status (CP: HR 3.6 p = 0.01; TE: HR 19.4 p < 0.01; renal: HR 2.4 p = 0.01) and for RFS (infectious: HR 2.1 p < 0.01; renal: HR 3.2 p < 0.01). Conclusions: Major complications after proctectomy for cancer are associated with decreased recurrence-free and overall survival. Given the association of infectious complications and postoperative renal dysfunction with earlier recurrence of disease, efforts must be directed towards defining best practices and standardizing care.