No consensus exists on using a specific screening tool to assess malnutrition in critically ill patients. Thus, we assessed malnutrition in intensive care unit (ICU) patients by comparing similarity of results between the Malnutrition Universal Screening Tool (MUST) and Phase Angle (PhA) measured by Bioelectrical Impedance Analysis. A cross-sectional observational study of 321 patients examined their nutritional status at least 1 week after the ICU admission using MUST, PhA, and anthropometric measurements. Diagnoses and Acute Physiologic Assessment and Chronic Health Evaluation II scores were retrieved retrospectively. The mean of Acute Physiologic Assessment and Chronic Health Evaluation II score was 17.73, indicating moderate morbidity. The majority of patients (71.0%) were fed enterally while the remaining (29.0%) did not have any nutritional intervention. Although the average body mass index was normal, only 55.3% of patients received the prescribed calories up to the day of assessment (median day of assessment was 11 [interquartile range: 9-18]). The MUST and PhA results showed that patients fell consistently into 3 malnutrition levels. Hierarchical Multiple Regression revealed that MUST (risk of malnutrition) explained an additional 44.9% of the variance in PhA (β: −.449, P < .001, confidence interval: −1.25 to −0.740). Although MUST measures malnutrition subjectively, it demonstrated higher congruency with Bioelectrical Impedance Analysis in the screening of malnutrition in this sample of critically ill patients.