In this study the authors report a case of Reye syndrome in a three year old patient. The most likely etiopathogenetic mechanisms are analysed and incidence, clinical features and diagnostic criteria are discussed. The possible association between the development of Reye's Syndrome and the use of salicylates, particularly aspirin, during the preceding viral infection (influenza or chicken pox) is emphasized. We underline the importance of early diagnosis that facilitates the successful management of Reye's Syndrome.