Background: Risk assessment for emergency laparotomy (EL) is important for guiding decision-making and anticipating the level of perioperative care in acute clinical settings. While established tools such as the American College of Surgeons National Surgical Quality Improvement Program calculator (ACS-NSQIP), the National Emergency Laparotomy Audit Risk Prediction Calculator (NELA) and the Portsmouth Physiological and Operative Severity Score for the enumeration of Mortality and Morbidity calculation (P-POSSUM) are accurate predictors for mortality, there has been increasing recognition of the benefits from including measurements for frailty in a simple and quantifiable manner. Psoas muscle to 3rd lumbar vertebra area ratio (PM:L3) measured on CT scans was proven to have a significant inverse association with 30-, 90- and 365-day mortality in EL patients. Methods: A retrospective analysis was conducted of 500 patients admitted to four Australian hospitals who underwent EL during 2016–2017, and had contemporaneous abdomino-pelvic CT scans. Radiological sarcopenia was measured as PM:L3 ratios. ASC-NSQIP, NELA and P-POSSUM were retrospectively calculated. Univariate and multivariate logistic regression modelling was used to assess these ratios and scores, as well as American Society of Anaesthesiologists (ASA) classification separated into ASA I-III and IV/V (simplified ASA), as potential predictors of 30-, 90- and 365-day mortality. Results: PM:L3, simplified ASA, ACS-NSQIP, NELA and P-POSSUM were each statistically significant predictors of 30-day, 90-day and 365-day mortality (P < 0.001). Logistic regression models of 30-, 90- and 365-day mortality combining PM:L3 (P = 0.001) and simplified ASA (P < 0.001) exhibited AUCs of 0.838 (0.780, 0.896), 0.805 (0.751, 0.860) and 0.775 (0.729, 0.822), respectively, which were comparable to that of ACS-NSQIP and NELA. Conclusion: Combining the semi-physiological parameter ASA classification with PM:L3 provides a quick and simple alternative to the more complex established risk assessment scores and is superior to PM:L3 alone.