Computed tomography (CT) can be used for accurate estimation of whole-body muscle mass and muscle density and for detection of sarcopenia. The goal of this study was to evaluate the additional value of CT measured sarcopenia and muscle attenuation alongside the Malnutrition Universal Screening Tool (MUST) for the prediction of post-operative morbidity after oncological colorectal resection, whilst correcting for known risk factors. A prospective cohort study of 80 patients undergoing elective colorectal surgery in the Netherlands. Patients were screened for nutritional risk upon admission using the MUST. Additionally, preoperative CT scans were used to determine skeletal muscle mass for the detection of sarcopenia and muscle attenuation. Univariate and multivariable analyses were performed to evaluate associations between the MUST, muscle attenuation and sarcopenia on the one hand and post-operative complications measured by the Clavien-Dindo score on the other hand. American Society of Anesthesiology-classification (ASA) ≥3, age ≥70, MUST ≥2 and lower than median muscle attenuation were significantly associated with a higher risk for postoperative complications (Clavien-Dindo score ≥2) (p≤0.05), whereas sarcopenia was not (p=0.59). Multivariate analyses showed that only MUST ≥2 remained significantly associated with postoperative complications when corrected for age (p=0.03, OR 5.8, 95%CI 1.1-29.6), but not when corrected for age ≥70 and ASA ≥3. Muscle attenuation and sarcopenia were not significantly associated with postoperative complications. Our results suggest that using CT measured sarcopenia may have only little additional value over the MUST for the prediction of increased short-term post-operative morbidity after oncological colorectal surgery. It also underlines the importance of currently implemented easy-to-use nutritional screening tools (MUST) and raises the question of the evaluation of muscle quality versus quantity in body composition imaging. However, further research is needed to investigate the role of sarcopenia for predicting outcome after colorectal surgery, and investigate the role of muscle attenuation measurements for the prediction of muscle function. CATEGORY OF SUBMISSION: observational study.