Poor nutrition is an underrecognized cause of significant morbidity in hospitalized children. 1,2 In addition to presenting with poor nutrition at the time of admission, children often suffer worsening of their nutritional status during the course of a hospitalization, 3,4 often due to providers' underrecognition of ongoing poor intake (see Fig 1). Pediatric hospitalists can and should play a central role in recognizing and treating this common comorbid condition. In this article we highlight the important issue of malnutrition in hospitalized pediatric patients and propose a general approach to nutritional assessment and supplementation for the pediatric hospitalist. DEFINITION OF MALNUTRITION Malnutrition is defined as a state in which a deficiency (or excess) of energy, protein, and other nutrition causes measurable adverse effects on the body and on growth (in children), and may impact clinical outcome. 5 The term "nutritional deterioration" has been used to describe significant weight loss in hospitalized children, a precursor to acute malnutrition. Although the term malnutrition includes both overnutrition (obesity) and undernutrition, in this article we focus specifically on undernutrition. MALNUTRITION IN HOSPITALIZED CHILDREN: INCIDENCE AND OUTCOMES Recent studies in developed countries have estimated the prevalence of malnutrition in hospitalized children as 12% to 24%. 1,3,5,6 Despite many medical advances over the past 20 years, the prevalence of malnutrition among hospitalized children has not decreased. Malnutrition is known to have detrimental effects on clinical outcomes. 7 For example, in children with bronchiolitis in PICUs, poor nutritional status is significantly related to increased length of stay and duration of mechanical ventilation. 2 Malnourished children experience more complications, such as infections after surgery, than well-nourished children, also leading to increased length of stay. 8 Malnutrition also affects growth. Growth depends on a permanent increase in fat and lean body mass, which requires positive energy and nitrogen balance. 7 An increase in nutritional demands due to illness or injury competes with these specific needs of growth. Infancy and adolescence are especially high-risk periods when sustained undernutrition during illness may inhibit growth. Initially, children may show an absence of weight gain,