Background: Malnutrition is one of the major problems during the stay in the intensive care units (ICUs). Critically ill patients are at high risk of developing malnutrition, associated with worse clinical outcomes. This work aimed to detect the severity of malnutrition in critically ill patients by using the Subjective Global Assessment score (SGA) and its association with the length of ICU stay and mortality. Methods: This prospective cohort observational study was carried out on 50 patients aged >18 years old, both sexes, with clinical criteria of malnutrition, involuntary weight loss, low body mass index, decreased mass of muscles, history of decreased food intake or absorption and inflammation or acute disease or injury with severe inflammation. All patients were subjected to mid-arm circumference (MAC), triceps skin fold (TSF) and hand grip strength . Results: The mean length of stay in ICU was 13.5±11.2 days. 18 patients needed mechanical ventilation (MV) representing 36% of cases with mean ventilation days 10.7±7.1, and the mortality proportion 34%. A statistically substantial correlation existed between mortality, smaller MAC (P = 0.001), and TSF (P = 0.001). In addition, the Handgrip was lower in mortality but didn't reach statistical significance (P = 0.091). A substantial association existed between the advanced grade of SGA (grade C) and mortality (P = 0.001). Conclusions: There was a strong association between mortality in critically ill patients and smaller triceps skin fold, MAC. Severe malnutrition in critically ill patients SGA (grade C) was significantly associated with mortality and the need for MV .