Context The Eastern Cooperative Oncology Group/World Health Organization Performance Status (ECOG/WHO PS) is a prognostic factor. It should be used in analyzing health outcomes such as risk-adjusted hospital performance models in cancer populations. Performance status is rarely recorded in surgery, often the place where cancer is first diagnosed. Could a universally collected preoperative measure be substituted for ECOG/WHO PS? Objectives The aim of this study was to assess whether the American Society of Anesthesiologists (ASA) score could be used as a proxy for ECOG/WHO PS in risk adjustment models predicting extended length of stay (LOS) after cancer surgery. Methods Data were obtained from the BioGrid Colorectal Cancer Database for 2540 treatment episodes (2528 patients) at five hospitals in Victoria and Tasmania, Australia, from 2003 to 2012. Using extended LOS as the index outcome measure, a risk adjustment model was developed using patient demographic and clinical variables. The ECOG/WHO PS and ASA score were added to this model, and the relative percentage change in hospital coefficients were examined. Model fit was compared using Akaike's information criterion (AIC) and concordance statistic (c). Results Adding ECOG/WHO PS or ASA score to the model resulted in relative changes in the hospital coefficients of up to 27%. The ECOG/WHO PS and ASA score performed similarly, with addition of either improving the AIC from 988.2 to 976.3. Inclusion of both measures further improved AIC to 972.4. Conclusion The ASA score can be used as a proxy for ECOG/WHO PS in risk adjustment models predicting cancer surgery. Further studies should assess its broader application for other outcomes and in other settings.