Aim <p>This study aimed to explore the association between the geriatric nutritional risk index (GNRI) and the risk of mortality in critically ill older patients with community-acquired pneumonia (CAP).</p> Methods <p>This retrospective study included 1924 critically ill patients with CAP from the Medical Information Mart for Intensive Care-IV3.1 (MIMIC-IV3.1) database. The participants were grouped into four groups based on GNRI levels. The clinical outcome was 30-day, 90-day, 180-day, and 1-year mortality. Cox proportional hazards regression analysis and restricted cubic spline regression were used to evaluate the association between the GNRI and clinical outcomes in critically ill older patients with CAP.</p> Results <p>A total of 1924 patients (56.9% male) were included in the study. The 30-day, 90-day, 180-day, and 1-year mortality were 37.7%, 47.7%, 54.0% and 59.1%, respectively. Multivariate Cox proportional hazards analysis showed that the GNRI was independently associated with all-cause mortality. After adjusting for confounders, GNRI remained significantly associated with both short- and long-term mortality. Restricted cubic splines revealed a linear association between GNRI and all-cause mortality in CAP patients.</p> Conclusion <p>Our study indicates that the GNRI has a significant association with all-cause mortality in critically ill older patients with CAP. However, further confirmation of these findings requires larger prospective studies.</p>