Background The role of the geriatric nutritional risk index (GNRI) as a prognostic factor in intensive care unit (ICU) patients with acute kidney injury (AKI) remains uncertain. Objectives The aim of this study was to investigate the impact of the GNRI on mortality outcomes in critically ill patients with AKI. Methods For this retrospective study, we included 12,058 patients who were diagnosed with AKI based on ICD-9 codes from the eICU Collaborative Research Database. Based on the values of GNRI, nutrition-related risks were categorized into four groups: major risk (GNRI < 82), moderate risk (82 <= GNRI < 92), low risk (92 <= GNRI < 98), and no risk (GNRI >= 98). Multivariate analysis was used to evaluate the relationship between GNRI and outcomes. ResultsPatients with higher nutrition-related risk tended to be older, female, had lower blood pressure, lower body mass index, and more comorbidities. Multivariate analysis showed GNRI scores were associated with in-hospital mortality. (Major risk vs. No risk: OR, 95% CI: 1.90, 1.54-2.33, P < 0.001, P for trend < 0.001). Moreover, increased nutrition-related risk was negatively associated with the length of hospital stay (Coefficient: -0.033; P < 0.001) and the length of ICU stay (Coefficient: -0.108; P < 0.001). The association between GNRI scores and the risks of in-hospital mortality was consistent in all subgroups. Conclusions GNRI serves as a significant nutrition assessment tool that is pivotal to predicting the prognosis of critically ill patients with AKI.