Anastomotic leakage is still the most frequent cause of postoperative mortality following esophageal and cardial surgery. The German Advanced Surgical Study Group recommended that endoscopy should be the first diagnostic method if leakage is suspected. The German Surgical Endoscopy Association developed and validated adefinition and severity classification of anastomotic leakage following esophageal and cardial resection. In 2010 the international study group on insufficiency published adefinition and severity grading of anastomotic leakage following anterior resection of the rectum, which was validated in 2013. The severity of anastomotic leakage should be graded according to the impact on clinical management: typeI requires only conservative management, typeII requires interventional radiological or endoscopic treatment and type III requires surgical revision. In contrast to the rectal classification typeIII is divided into acategory without (typeIIIa) or with (typeIIIb) conduit resection and diversion. The validation was carried out on a10-year collective from the university hospitals in Heidelberg and Tübingen. From 2006-2015 all 92patients who developed an anastomotic leakage following esophageal and cardial resection were enrolled in the study. We found asignificant increase in the length of stay in the intensive care unit (ICU) with increasing classification type (p < 0.0143). Furthermore, there was a significant correlation with the general classification of postoperative complications according to Clavien-Dindo as well as with mortality (p < 0.001). Standardized parameters are the prerequisite to be able to compare the results between hospitals and studies. The validation of the suggested classification shows that the differentiation between the groups is substantiated by the correlation to the length of ICU stay, Clavien-Dindo and mortality and will therefore contribute to abetter comparability of data on leakage following esophageal resection in the future.