Objective:This nation-wide population-based study aimed to report postoperative morbidity and mortality after esophagectomy and gastrectomy in the Netherlands according to the definitions of the Esophagectomy Complications Consensus Group (ECCG).Background:To standardize international outcome reporting in esophageal surgery, the ECCG developed a standardized outcomes set.Methods:For this national cohort study, all patients undergoing esophagectomy or gastrectomy for cancer between 2016 and 2017 were selected from the Dutch Upper gastrointestinal Cancer Audit. In a random sample of hospitals, data completeness and accuracy were validated by reabstraction of the data. The investigated outcomes in the present study were postoperative complications, major complications (Clavien-Dindo grade ≥III), and 30-day mortality, according to definitions of the ECCG.Results:A total of 2545 patients from 22 hospitals were included. The completeness of the Dutch Upper gastrointestinal Cancer Audit was estimated at 99.8%. Data accuracy on different items was 94% to 100%. After esophagectomy, 1046 of 1617 patients (65%) had a postoperative complication including 468 patients (29%) with a major complication. Most common complications were pneumonia (21%), esophago-enteric leak from anastomosis, staple line or localized conduit necrosis (19%), and atrial dysrhythmia (15%). The 30-day mortality was 1.7%. After gastrectomy, 397 of 928 patients (42%) had a postoperative complication including 180 patients (19%) with a major complication. Most common complications were pneumonia (12%), esophago-enteric leak from anastomosis, staple line or localized conduit necrosis (9%), and acute delirium (5%). The 30-day mortality was 4.4%.Conclusions:Reporting complications according to the ECCG platform is feasible in the Netherlands and facilitates international benchmarking.