Reye's syndrome or encephalopathy with fatty infiltration of the liver occurs mainly in childhood and to a lesser degree in adult age. Salicylate may play a role in the pathogenesis of this syndrome. Still's disease is a form of juvenile rheumatoid arthritis very rare in the adult. A case is reported of a 39-year old woman who developed Reye's syndrome while on aspirin therapy for the treatment of a classical adult Still's disease.