The aim of the present study was to investigate whether nutritional status and changes in muscle and adipose tissue determined by computed tomography are predictors of mortality in hospitalized patients. This was a prospective cohort study involving patients ≥ 20 years of age hospitalized in a public hospital. Sociodemographic and clinical variables were collected from electronic medical records. Nutritional variables were determined. All patients were followed prospectively until the hospital outcome, which could be discharge or death. Body composition was defined from computed tomography images, with the identification of myopenia, myosteatosis, and myopenic obesity. The sample comprised 542 patients. The mortality rate was 10.7% (95% CI: 6.4-15.0%). The independent predictors of mortality were malnutrition, assessed with the subjective global assessment (hazard ratio: 4.18; 95% CI: 1.01-17.22; p = 0.047), and myopenic obesity (hazard ratio: 2.82; 95% CI: 1.11-7.20; p = 0.029). The findings of the present study add to the limited evidence in the literature that body composition is associated with outcomes in hospitalized patients.