A study was made of 443 surgical patients using a standard protocol for nutritional evaluation based on anthropometrical, analytical and immunological tests. The main criteria used for considering the presence of malnutrition was a weight loss of 10% and/or seric albumin level of less than 3.5 g/dl., by which method four nutritional groups were established. The average age of the sample was 56 +/- 15 years and 35% of patients had neoplasias, 9.25% of patients were classified as belonging to Group A (weight loss and low albumin levels), 10.15% as group B (low albumin levels), 14.44% as group C (weight loss), and 66.16% as group D (normal), so that the global malnutrition percentage was 33.84%. The Body Mass Index (BMI) and Ideal Weight Percentage (% IWP) were of similar importance, and there was a significant alteration in the Triceps Skin Fold (% TSF) and Muscular Area Percentage of the arm (% MAP) when malnutrition was in evidence. In the study of the Delayed Hypersensitivity Skin Tests (DSST) 21.4% showed anergia, 15.8% hypoergia and 62.8% were reactive, with a reduction in reactivity in the case of malnutrition. This was the parameter that most affected the albumen level.