Cow milk-sensitive enteropathy is a temporary disorder of infancy characterized by a variably abnormal small intestinal mucosa while milk is in the diet. This abnormality is reversed by a cow milk-free diet, only to recur on challenge. Important predisposing factors are age (< 3 years), transient IgA immunodeficiency, atopy, and early bottle feeding. The disorder is diagnosed histologically by evidence of mild-to-moderate partial villous atrophy with thin, often patchy mucosa. For an accurate clinical diagnosis, challenge with the offending food after a demonstrated response to cow milk elimination is critical. When available, serial small intestinal bowel biopsies related to elimination and challenge are also important. Treatment is elimination of cow milk and all foods based on cow milk, and substitution of cow milk feedings with commercially available formulas free of cow milk protein. Five types of cow milk substitutes are described; only nutritionally complete formulas are recommended. Later, a milk challenge will determine the timing of safe reintroduction of cow milk to the diet, at a time when the child is gaining weight, thriving, and symptom free. This dietary treatment is always temporary; reintroduction of a normal diet is nearly always possible between 1 and 2 years of age.