Reye's syndrome is a rare but potentially fatal disease that affects all organs of the body, with an especially devastating attack upon the liver and brain. It is characterized by encephalopathy with severe edema of the brain, increased intracranial pressure, hypoglycemia, and fatty infiltration of the liver. It is a two-phase illness, almost always associated with a previous viral infection. Studies strongly support a link between the use of aspirin and Reye's syndrome. Reported cases are on the decline. Recent epidemiologic studies show the incidence for children 10 to 19 years old to be stable, but reduced for younger children. Special attention needs to be directed toward educating adolescents and parents of older children about Reye's syndrome and cautioning against the use of aspirin to treat influenza, upper respiratory infections, or varicella.