Protein-energy wasting (PEW), defined as reduced somatic and/or circulating body protein mass, decreased fat mass, and usually reduced protein and energy intake, has a prevalence that is variously estimated to be 18% to 75% in maintenance hemodialysis and chronic peritoneal dialysis patients. PEW is associated with increased morbidity and mortality and often is preventable or treatable. Thus, it has been argued that maintenance hemodialysis and chronic peritoneal dialysis patients should be monitored routinely for PEW and treated for this condition, when it occurs. A trend toward PEW can emerge in early stage 3 chronic kidney disease with an increasing risk toward the development and worsening of PEW as chronic kidney disease progresses. A main cause of PEW is inflammation, which may occur with or without clinically evident illness and can be associated with the most severe forms of PEW. Another major cause of PEW is decreased nutrient intake relative to the patient's nutritional needs, and may be caused by anorexia, which may be engendered by uremic toxicity, emotional depression, medications, or inflammatory disorders. Nonanorexic causes of reduced nutrient intake include inadequate finances to purchase or prepare foods; medical or surgical illnesses that impair the person's ability to ingest, digest, assimilate, or process the nutrients; impaired cognitive function; other mental or physical disabilities; and loss of dentures. Losses of nutrients during dialysis treatments or in urine (eg, the nephrotic syndrome), acidemia, and hormonal disorders can contribute to the development of PEW. Early initiation and adequate doses of renal replacement therapy, rapid treatment of reversible inflammatory processes, ensuring an adequate nutrient intake, and prevention of acidemia may be used to prevent and treat PEW.