Malnutrition is an important factor which influences both the morbidity and the recovery. Assessment of the initial nutritional status, then its evolution during the disease and/or treatment, plays an important role for tailoring the nutritional support. This assessment allows to specify the nutritional needs and body reserves, as well as the metabolic and immunologic functions. The global nutritional assessment is aimed at defining if the patient is: well nourished, slightly or severely malnourished, and if the aetiologies of the existing malnutrition will disappear, increase or decrease. This conclusion correlates the nutritional assessment to the dynamic of the pathology and highlights if the nutritional support has to be immediate or delayed, maximal or partial. No single method allows to detect PCM, except in very severe cases. The diagnosis of PCM results of various clinical, biological and functional informations. This review describes the main methods and suggests practical modalities for nutritional assessment.