The post-viral syndrome is described and its aetiology is discussed. Many features of the syndrome point to hysteria and altered medical perception as causes but much evidence for organic disease is also presented. Current interest focuses on recent or persisting infection with Coxsackie viruses. A balanced view of the syndrome as a mixture of organic and psychiatric dysfunction is offered. Widely differing estimates of incidence are quoted, possibly owing to varying medical awareness of the syndrome. Many drug therapies have been tried without success and management of the post-viral syndrome is hampered by the reluctance of patients to accept psychiatric support once the diagnosis is known. Many names have been proposed for the syndrome, some implying a purely physical or purely psychogenic aetiology: post-viral syndrome is suggested as the most appropriate term. Increased awareness of the syndrome will lead to an increase in its diagnosis in general practice: the role of the Myalgic Encephalomyelitis Association in promoting a combined psychiatric and organic view of the disease among sufferers is emphasized.