Background: More than age, patient comorbidity is increasingly considered as the prominent predictor of postoperative mortality (POM) in esophageal and gastric cancer surgery, leading a growing number of elderly to be operated on. However, the respective impact of age and comorbidity on POM remains to be elucidated. The study objective was to investigate the impact of age on POM according to patient comorbidity. Methods: All consecutive patients who underwent esophageal or gastric cancer surgery between 2010 and 2012 in France were included (n = 11,196). The 30-day POM was compared by age groups (20-39, 40-59, 60-79, ≥ 80) and stratified according to the Charlson score (0, 1-2, ≥ 3). The consistency across esophageal (n = 3286) and gastric (n = 7910) subgroups and variations between 30-day and 90-day POM were analyzed. Results: Patients ≥ 60 years represented 73.8% of cases. A linear increase in 30-day and 90-day POM was observed with increasing age, with rates of 0.9% and 2.1%, 2.4% and 5.4%, 4.8% and 8.8%, and 9.3% and 15.9% in 20-39, 40-59, 60-79, ≥ 80 years age groups, respectively (P< 0.001). Comparing 20-39 and ≥ 80 years age groups, 30-day POM was 1.0% vs. 7.0% for Charlson 0 (P< 0.001), 3.1% vs. 11.1% for Charlson1-2 (P< 0.001) and 0% vs. 19.5% for Charlson ≥ 3 (P= 0.020) patients. A similar linear increase of POM by growing age groups was observed for 90-day POM and in esophagus and stomach subgroups. By multivariable analysis age groups (OR 1.03 95%CI 1.02-1.04, p < 0.001) and Charlson score (OR 1.56 95%CI 1.43-1.70, p < 0.001) were independent predictors of POM. Conclusions: Age and patient comorbidity have a similar and cumulative impact on POM after esophageal and gastric cancer surgery.