The assessment of nutritional status of patients should rely on sensitive and specific evaluation tools. However a universally recognized criterion of severity of denutrition is still lacking. The most important clinical indicator is the weight. The speed of weight loss is an important point to consider: a loss of 2% within one week is equivalent to 5% in one month and 10% in six months. Other anthropometric indices such as the triceps skin fold and the mid arm muscle circumference have not shown, when considered alone, to increase the risk carried by denutrition. Therefore other clinical indicators have to be considered, the association of which is suggestive of malnutrition, but none when considered alone is neither specific nor pathognomonic. Food intake is quantified by questioning. Among the biological markers representative of the pool of circulating visceral proteins is albumin. Numerous studies have demonstrated a morbidity and mortality increase when the plasmatic albumin concentration is less than 30 g.L-1. Other proteins with a shorter half-life, such as transferin, prealbumin and retinal binding protein have been recommended. The determination of muscular mass is also a tool for nutritional assessment. The muscular function and immunologic tests such as the lymphocyte count and cutaneous reactivity to various antigens have been assessed as denutrition indices. The determination of body mass composition by bioelectrical impedance could become the technique of choice for nutritional assessment. However its use for peri-operative evaluation has not been validated prospectively. Because of the lack of reliability of markers when considered alone, several authors produced multivariate nutritional indices.(ABSTRACT TRUNCATED AT 250 WORDS)