<p>Pre-operative risk assessment tools and frailty scores are increasingly common due to the growing number of elderly, comorbid and frail patients. This study aims to assess the performance of the ACS-NSQIP-SRC (American College of Surgeons- National Surgical Quality Improvement Program- Surgical Risk Calculator) and the 5mFI (5-items modified Frailty Index) in predicting clinical outcomes after emergency cholecystectomy. This is a retrospective cohort study of patients with acute calculous cholecystitis admitted at our tertiary care center from 2018 to 2023. We evaluated discrimination, calibration, and accuracy of the ACS-NSQIP-SRC and 5mFI in predicting any complication, mortality, length of hospital stay (LOS), need for readmission and supported discharge (30-day follow-up). Among 365/642 patients who underwent surgery, the 5mFI showed poor discrimination for all outcomes but good overall accuracy in the prediction of a supported discharge. In 198 operated patients with available data for the ACS-NSQIP-SRC, it underestimated complications and need for readmission while overestimated the need for supported discharge. There was no concordance between predicted and observed LOS. Among 277/642 patients undergoing non-operative management, 2/3 were frail or mild frail and had a predicted rate of any unfavorable outcome after surgery between 0 and 20%, being 95% above the average risk of each outcome. Mortality couldn’t be studied because no death was reported. ACS-NSQIP-SRC and 5mFI performance in predicting outcomes after emergency cholecystectomy for acute cholecystitis was poor. In the emergency cholecystectomy setting, the ACS-NSQIP-SRC may be less informative, and the 5mFI may be excessively simplistic by neglecting the multidimensional nature of frailty.</p> Graphical Abstract <p></p>