Background: Malnutrition is an important factor in the survival of critically ill patients. The purpose of the present study was to assess the nutritional status of patients in the intensive care unit (ICU) on the days of admission and discharge via a detailed nutritional assessment. Methods: Totally, 125 patients were followed up from admission to discharge at 8ICUs in Shiraz, Iran. The patients’ nutritional status was assessed using subjective global assessment (SGA), anthropometric measurements, biochemical indices, and body composition indicators. Diet prescription and intake was also evaluated.Results: Malnutrition prevalence significantly increased on the day of discharge (58.62%) compared to the day of admission (28.8%) according to SGA (P<0.001). The patients’ weight, mid-upper-arm circumference, mid-arm muscle circumference, triceps skinfold thickness, and calf circumference decreased significantly as well (P<0.001). Lean mass weight and body cell mass also decreased significantly (P<0.001). Biochemical indices showed no notable changes except for magnesium, which decreased significantly (P=0.013). A negative significant correlation was observed between malnutrition on discharge day and anthropometric measurements. Positive and significant correlations were observed between the number of days without enteral feeding, days delayed from ICU admission to the commencement of enteral feeding, and the length of ICU stay and malnutrition on discharge day. Energy and protein intakes were significantly less than the prescribed diet (26.26% and 26.48%, respectively).Conclusion: Malnutrition on discharge day increased in the patients in the ICU according to SGA. Anthropometric measurements were better predictors of the nutritional outcome of our critically ill patients than were biochemical tests.