Protein energy malnutrition (PEM), the most widespread nutritional deficiency disorder of mankind, is a group of related disorders, with a more complex and still incompletely understood etiologic basis than its name suggests. Dermatologic and other clinical manifestations are more florid and characteristic in kwashiorkor than in marasmus. The complex of clinical syndromes that constitute PEM is best considered when using a three-dimensional model to illustrate its varying degrees (ie, mild, moderate, or severe) and the spectrumlike nature of the forms of the severe degree (ie, kwashiorkor, marasmic-kwashiorkor, or marasmus). Protein energy malnutrition is not confined to children in the Third World and is the most common form of undernutrition in hospitalized patients in Western countries. Marasmus is by far the most prevalent form. Much of the nutritional support given in hospitals is not based on an assessment of nutritional status, and little attention is paid to the different forms PEM might take. Even those who do consider this last point confuse hypoalbuminemia in patients acutely stressed or infected with kwashiorkor. Recent evidence suggests that the skin changes of kwashiorkor may be caused by zinc deficiency. Almost nothing is known about the histopathology of the skin per se in PEM but studies of the hair bulb have shown important differences among patients with kwashiorkor, marasmus, and normal skin.