Malnutrition (MN) continues to be an unacknowledged and underestimated problem in hospitals. It affects patients, by increasing complications, mean hospital stay (HS) and health-related risks. Such MN tends to be aggravated by hospitalization. Our purpose was to analyze the influence of hospitalization on the nutritional status of the patients studied. The following data were collected from 134 patients previously assessed for malnutrition risk between the 3rd and 5th day after admission: 1) during admission: type of diet, no of days with an absolute diet, use of protein supplements and artificial nutrients, onset of large-scale and small-scale complications, duration of HS, no of subsequent admissions and death; and 2) on discharge: serum albumin (SA) g/dl, total lymphocytes (TL)/ml. A statistical analysis was carried out using the chi 2 test, a Correlation test and ANOVA for a significance level of p < 0.05. It was possible to review 71.64% of the case histories and 61.45% were assessed. The following findings were reached: 1) the patients with weight loss on admission (WLA) had lower SA figures on discharge (p < 0.01) and a higher mortality rate (p < 0.001). 2) Absolute diet during HS led to a lengthening of admission time (p < 0.001). 3) Those patients with a severe risk of MN were the same ones who only received nutritional support (p < 0.001). 4) Patients who were re-admitted presented a worse nutritional status on discharge (p < 0.001). 5) An increase of 3.7 days in the HS in medical cases and 7.9 days more in surgical services, for those patients at risk of MN. 1. Low SA, TL and WLA figures are prognostic factors for hospital death. 2. Nutritional support was only used at severe levels of MN risk, so the HS was longer in these cases. 3. Patients with MN should be detected on arrival in order to avoid inherent health risks during hospitalization.