We describe four Italian adolescents in whom a persistent, debilitating fatigue appeared after therapeutic ingestion of products containingl-tryptophan and subsequent to the development of a transient rise in eosinophil count and severe myalgia (Eosinophilia Myalgia Syndrome-EMS). Their clinical picture was indistinguishable from that of the socalled Chronic Fatigue Syndrome. A chronic fatigue may occur after diverse triggering agents and it represents the peculiar clinical evolution of these four paediatric cases of EMS.