Protein-energy malnutrition (PEM) is a common phenomenon in maintenance dialysis (MD) patients and a risk factor for poor quality of life and increased morbidity and mortality, including cardiovascular death, in these individuals. The association between undernutrition and adverse outcome in MD patients, which stands in contrast to that seen in the general population, has been referred to as reverse epidemiology. Measures of food intake, body composition tools, nutritional scoring systems, and laboratory values are used to assess the degree of severity of PEM, but no uniform approach is available for rating the overall severity of PEM. Epidemiologic studies suggest that inflammation is a missing link between PEM and poor clinical outcome in MD patients, and the existence of a malnutrition inflammation complex syndrome is suggested in these patients. Inflammation may be due to subclinical and clinically apparent illnesses. Some investigators suggest that PEM may predispose to illness and inflammation. There is a paucity of information concerning the effect of nutritional therapy on morbidity and mortality in MD patients. Interventional studies of the effect of nutritional support on outcome often are difficult to interpret because of small sample sizes, short duration of study, and other limitations. Large-scale, randomized, clinical trials of the effects of nutritional intake, nutritional status, and inflammation on clinical outcome are needed to define better the relationships between these factors in MD patients. © 2001 by the National Kidney Foundation, Inc.