Background: Postoperative complications (POCs) can negatively impact survival after oncologic resection. POCs may also decrease the rate of adjuvant therapy completion. We evaluated the impact of complications on gastric cancer survival and analyzed the combined effect of complications and adjuvant therapy on survival. Methods: We analyzed 824 patients from 7 institutions of the U.S. Gastric Cancer Collaborative who underwent curative resection for gastric adenocarcinoma between 2000 and 2012. POC were graded using the modified Clavien–Dindo system. Survival probabilities were estimated using the method of Kaplan and Meier and analyzed using multivariate Cox regression. Results: Median follow-up was 35 months. The overall complication rate was 41 %. The 5-year overall survival (OS) and recurrence-free survival (RFS) of patients who experienced complications were 27 and 23 %, respectively, compared with 43 and 40 % in patients who did not have complications (p < 0.0001 for OS and RFS). On multivariate analysis, POC remained an independent predictor for decreased OS and RFS (HR 1.3, 95 % CI 1.1–1.6, p = 0.03 for OS; HR 1.3, 95 % CI 1.01–1.6, p = 0.03 for RFS). Patients who experienced POC were less likely to receive adjuvant therapy (OR 0.5, 95 % CI 0.3–0.7, p < 0.001). The interaction of complications and failure to receive adjuvant therapy significantly increased the hazard of death compared with patients who had neither complications nor adjuvant therapy (HR 2.3, 95 % CI 1.6–3.2, p < 0.001). Conclusions: Postoperative complications adversely affect long-term outcomes after gastrectomy for gastric cancer. Not receiving adjuvant therapy in the face of POC portends an especially poor prognosis following gastrectomy for gastric cancer.