Technical Abstract: Critical illness has a major impact on the nutritional status of both children and adults. A retrospective study was conducted to evaluate the incidence of hospital malnutrition at a pediatric tertiary intensive care unit (PICU). Serum concentrations of IL-6 in subgroups of well-nourished and malnourished patients were also evaluated in an attempt to identify those with a potential nutritional risk. A total of 1077 patients were enrolled. Nutritional status was evaluated by Z-score (weight for age). We compared mortality, sepsis incidence, and length of hospital stay for nourished and malnourished patients. We had a subgroup of 15 patients with severe malnutrition (MN) and another with 14 well-nourished patients (WN). Cytokine IL-6 determinations were performed by enzyme-linked immunosorbent assay. Fifty-three percent of patients were classified with moderate or severe malnutrition. Similar amounts of C- reactive protein (CRP) were observed in WN and MN patients. Both groups were able to increase IL-6 concentrations in response to inflammatory systemic response, and the levels followed a similar evolution during the study. However, the mean values of serum IL-6 were significantly different between WN and MN patients across time, throughout the study (p = 0.043). A considerable proportion of malnourished patients need specialized nutritional therapy during an intensive care unit (ICU) stay. Malnutrition in children remains largely unrecognized by healthcare workers on admission. The incidence of malnutrition was very high. Malnourished patients maintain the capacity to release inflammatory markers such as CRP and IL-6, which can be considered favorable for combating infections. On the other hand, this capacity might also have a significant impact on nutritional status during hospitalization.