BACKGROUND: Sepsis-associated delirium (SAD) is a common complication in intensive care unit (ICU) patients and is associated with increased mortality. Frailty, characterized by diminished physiological reserves, may influence the development of SAD, but this relationship remains poorly understood. AIMS: To comprehensively analyze the assessment of frailty as a predictive factor for sepsis-associated delirium in older adults. METHODS: A retrospective cohort analysis was performed on sepsis patients aged ≥ 65 years admitted to the ICU. Frailty was assessed using the Modified Frailty Index based on 11 items including comorbidities and functional status. Patients were categorized into non-frail (MFI: 0-2) and frail (MFI ≥ 3) groups. Delirium was assessed using the ICU Confusion Assessment Method (CAM-ICU) and retrospective nursing notes. Logistic regression analysis was used to examine the relationship between frailty in older patients and the risk of delirium, and odds ratios (OR) and their 95% confidence intervals (CI) were calculated. RESULTS: Among 11,740 patients (median age approximately 76 years [interquartile range: 70.47-83.14], 44.3% female), frail patients tended to have longer ICU stays, higher severity scores, and potentially worse clinical outcomes. The study found a significant positive association between MFI and the risk of developing SAD (OR: 1.13, 95% CI: 1.09-1.17, p < 0.001). Additionally, frail patients had a higher risk of developing SAD compared to non-frail patients (OR: 1.31, 95% CI: 1.20-1.43, p < 0.001). CONCLUSIONS: Frailty independently predicts SAD development in older adults with sepsis in the ICU, emphasizing the importance of early recognition and prevention.