Reye's syndrome (encephalopathy and fatty liver) is generally considered a disease of children. Four patients, aged 16, 18, 19, and 23 years, with Reye's syndrome were initially seen by internists. A viral prodrome followed by vomiting and encephalopathy without focal neurological signs or jaundice clinically suggested Reye's syndrome. Normal findings of CSF examination (except for increased opening pressure), abnormal findings of liver function tests, and increased blood ammonia further supported the diagnosis. None was hypoglycemic. Reye's syndrome was related to influenza B virus in three patients and to Varicella in another. Three patients survived. Reye's syndrome may be seen intially by general practitioners, emergency room physicians, internists, or psychiatrists. The importance of considering this syndrome in the differential diagnosis of unexplained encephalopathy in adults is stressed.