INTRODUCTION Malnutrition, known as a cause of morbidity, has not been studied in children admitted to pediatric intermediate care units. This study aimed to describe the association between patients' nutritional status and the relative severity of illness that characterizes this population. PATIENTS AND METHODS In this prospective longitudinal study, a dedicated nutrition support team assessed the nutritional status of all children, aged 5 days to 18 years, admitted to our university pediatric intermediate care unit (Hôpital Femme-Mère-Enfants, Lyon, France) over one year (2012-2013). Weight, height, body mass index, weight-for-age ratio, height-for-age ratio, and the analysis of growth curves were collected at admission. We monitored patients' weight, which allowed us to detect malnutrition occurrence during the stay, and its progression up to 3 months after discharge. RESULTS A total of 459 patients were enrolled. Based on the analysis integrating all nutritional indices and the progression of growth curves, malnutrition at admission was detected in 23.8% of children (20.5% and 6.8% suffered from acute and chronic malnutrition, respectively). Based only on the body mass index, malnutrition was detected in 15.5% of children. Chronic disease appeared as a risk factor for malnutrition at admission (P=0.0001) and young age for acute malnutrition (P=0.04). The incidence of acquired malnutrition during the stay (in children with a length of stay > 5 days) was up to 26%, and dyspnea was the only risk factor identified. This population recovered with a normal nutritional status late (66% after 2 months and 16% after 3 months). CONCLUSIONS The prevalence of malnutrition is high in our pediatric intermediate care unit. The occurrence of acquired malnutrition during the stay is frequent. All children should benefit from systematic nutritional assessment at admission as well as careful monitoring during the stay and after discharge, to adapt early and individualized nutritional support.