Background: The aim of this study was to determine whether or not the short- and long-term outcomes were affected by the age-adjusted Charlson comorbidity index (ACCI) in patients who underwent curative resection for gastric cancer.Methods: The patients were retrospectively selected from among the medical records of consecutive patients who underwent curative gastrectomy with nodal dissection for gastric cancer at Yokohama City University and Kanagawa Cancer Center from January 2000 to August 2015.Results: A total of 2254 patients were eligible for inclusion in the present study. One thousand six hundred fifty-six patients had an ACCI of <6 points (ACCI low group), while 598 had a score of ≥6 points (ACCI high group). The median age (p<0.001) and American Society of Anesthesiologists physical status (ASA-PS) score (p<0.001) of the ACCI high group were higher in comparison to the ACCI low group. The incidence of surgical complications in the ACCI high group was significantly higher than that in the ACCI low group (12.0% vs. 7.2%, p<0.001). Univariate and multivariate analyses demonstrated that an ACCI high classification was a significant risk factor for postoperative complications. In addition, the 5-year OS rates of the ACCI low and ACCI high groups were 85.4% and 74.1%, respectively. The difference was statistically significant (p<0.001). The univariate and multivariate analyses demonstrated that an ACCI high classification was a significant prognostic factor for OS.Conclusions: Our results support that a high ACCI value is an independent risk factor for the short- and long-term outcomes of patients with gastric cancer. To improve the survival of patients with gastric cancer, it is necessary to carefully plan the perioperative care and the surgical strategy according to the ACCI.