Background: In order to determine the optimal combination of perioperative chemotherapy and chemoradiotherapy for Western patients with advanced resectable gastric cancer, the international multicentre CRITICS trial (ChemoRadiotherapy after Induction chemotherapy In Cancer of the Stomach) was initiated. In this trial, patients with resectable gastric cancer were randomised before start of treatment between adjuvant chemotherapy or adjuvant chemoradiotherapy following neoadjuvant chemotherapy plus gastric cancer resection. The purpose of this study was to report on surgical morbidity and mortality in this trial, and to identify factors associated with surgical morbidity. Methods: Patients who underwent a gastrectomy with curative intent were selected. Logistic regression analyses were used to assess risk factors for developing postoperative complications. Results: Between 2007 and 2015, 788 patients were included in the CRITICS trial, of whom 636 patients were eligible for current analyses. Complications occurred in 296 patients (47%). Postoperative mortality was 2.2% (n = 14). Complications due to anastomotic leakage was cause of death in 5 patients. Failure to complete preoperative chemotherapy (OR = 2.09, P = 0.004), splenectomy (OR = 2.82, P = 0.012), and male sex (OR = 1.55, P = 0.020) were associated with a greater risk for postoperative complications. Total gastrectomy and oesophago-cardia resection were associated with greater risk for morbidity compared with subtotal gastrectomy (OR = 1.88, P = 0.001 and OR = 1.89, P = 0.038). Conclusion: Compared to other Western studies, surgical morbidity in the CRITICS trial was slightly higher whereas mortality was low. Complications following anastomotic leakage was the most important factor for postoperative mortality. Important proxies for developing postoperative complications were failure to complete preoperative chemotherapy, splenectomy, male sex, total gastrectomy, and oesophago-cardia resection.