Sarcopenia and low skeletal muscle radiodensity (SMD) have been associated with adverse outcomes in patients with colorectal cancer (CRC); however, factors contributing to these 2 muscle abnormalities are unclear. The aim of this study was to investigate the association of medical and demographic characteristics with muscle abnormalities among patients with nonmetastatic CRC. Patients with stage I-III invasive CRC (2006-11) who had diagnostic computed tomography (CT) available from Kaiser Permanente Northern California electronic medical records were included. CT-assessed sarcopenia and low SMD were defined according to optimal stratification. Logistic regressions including age, stage, site, total adipose tissue (TAT), race/ethnicity, neutrophil-lymphocyte ratio, smoking history, alcohol use, and Charlson Comorbidity Score were performed to identify characteristics associated with muscle abnormalities. The study included 3262 patients (49.9% females) with a mean ± SD age of 62.6 ± 11.4 y. Sarcopenia and low SMD were highly prevalent (42.4% and 29.6%, respectively). Age and sex interactions were noted for muscle mass, but not SMD. Age was associated with higher odds of muscle abnormalities in a dose-response manner. Compared with those aged ≤50 y, patients aged 70-80 y had considerably higher odds (OR: 6.19; 95% CI: 4.72, 8.11) of sarcopenia, and low SMD (OR: 17.81; 95% CI: 11.73, 27.03). High TAT was related to a higher odds of low SMD (OR: 9.62; 95% CI: 7.37, 12.56), but lower odds of sarcopenia (OR: 0.59; 95% CI: 0.48, 0.71). Compared with Caucasians, African Americans had lower odds of sarcopenia and low SMD. Patients with a higher neutrophil-lymphocyte ratio had higher odds of having both muscle abnormalities. Patients who were smokers or had any comorbidity had higher odds of low SMD, but not sarcopenia. Muscle abnormalities were common in patients with nonmetastatic CRC, with great variability in muscle mass and SMD across age, TAT, and race/ethnicity. Factors associated with muscle abnormalities may be used to facilitate risk stratification and the guidance of targeted strategies to counteract these abnormalities.