The Gustave Roussy Immune (GRIm) score is aa prognostic marker in various cancer types. The aim of this study was to investigate the relationship between the GRIm score and short- and long-term outcomes in elderly patients with colon cancer. Patients aged ≥75 years who underwent colectomy between 2008 and 2019 were eligible for the study. Patients were divided into high GRIm (score 1-3) and low GRIm (score 0) groups. A total of 430 patients were enrolled (high GRIm, n=126; low GRIm, n=304). A high GRIm score was an independent predictive factor for postoperative complications [odds ratio=4.146; 95% confidence interval (CI)-2.536-6.777; p<0.001]. The median follow-up was 42 months (range=1-160 months). Five-year relapse-free (79.3% vs. 92.7%; p=0.001), overall (76.0% vs. 92.2%, p=0.001), and non-cancer-specific (84.7% vs. 94.6%, p=0.003) survival were lower in the high GRIm group. Multivariate analysis revealed a high GRIm score to be an independent predictive factor for poorer overall (hazard ratio=2.875; 95% CI=1.451-5.698; p=0.002) and non-cancer-specific (hazard ratio=3.650; 95% CI=1.612-8.265; p=0.001) survival. The GRIm score is useful for predicting postoperative complications and non-cancer cause of death in elderly patients and might be suitable as a surrogate marker for selecting candidates for surgery or perioperative treatment.