Abstract Objective. To assess the nutritional status of critically ill children and its modification after enteral nutrition. Design. Prospective observational study. Setting. Pediatric Intensive Care Unit of a University Hospital. Subjects. 42 critically ill children with mechanical ventilation. Interventions. At least four days of enteral nutrition. Endpoints. Change of nutritional status. Measurements and main results. Anthropometric [weight, height, cephalic circumference, skin fold thickness and nutritional indices], and biochemical [full blood count, glucose, cholesterol, triglycerides, free fatty acids, total proteins, albumin, prealbumin, fibronectine, transferrin, creatinine, urea, uric acid, aspartate aminotransferase, alanine aminotransferase, gamma-glutamyltransferase, alkaline phosphatase, nitrogen balance, and calculation of the height/creatinine index and of the stress index] nutritional assessment was carried out before starting the enteral nutrition, after 4 to 7 days, at 14 days, at 21 d...