Encephalopathy and fatty degeneration of the viscera (EFDV) is a common cause of death among children in northeastern Thailand. During a clinical and epidemiological study in 1969, 67 cases of EFDV were studied. Clinical features of this disease and Reye's syndrome were found to be similar. The incidence of the disease increases during the latter part of the rainy season. Almost all cases occur in children from rural areas. In Thailand, there is a geographic and seasonal association between the incidence of EFDV and the distribution of aflatoxin, indicating a possible etiologic relationship.