• The isolation of adenovirus from the liver of an infant with Reye's syndrome prompted a retrospective review to determine the role of this group of viruses in the cause of Reye's syndrome. A total of 34 patients with Reye's syndrome who were admitted to Vanderbilt University, Nashville, Tenn, during a ten-year period were identified. Six of the patients were younger than 1 year, and positive adenoviral cultures and increased serological responses were obtained in three of these children. The clinical and pathologic data from these three children suggest that adenovirus may be an important agent in initiating Reye's syndrome In the very young child. Further, the mitochondrial abnormalities present in the livers of the patients with adenovirus-associated disease tended to be mild in spite of severe clinical disease.