As reports of the occurrence of viral encephalitides from the Scandinavian countries have been few, the authors have reviewed an autopsy series from Rikshospitalet, Oslo, Norway. The investigation covered the years from 1952 to 1966, and 35 cases of probable virus encephalitis were collected. The cases could be separated into 4 groups according to clinical symptoms and histopathological picture. The first group corresponded well to the picture of an acute herpes simplex encephalitis with inclusion bodies, although the virus was isolated in brain tissue from the autopsy once only. In the second group the course of the illness varied greatly from 1 month up to nearly 8 years in 1 case. The histological findings were those of a diffuse subacute to chronic viral type of infection, and inclusion bodies were found in 6 of the cases including the one of 8 years' duration. The third group comprised acute and more prolonged cases, but the histopathological findings were sparse and uncharacteristic. The fourth group consisted of children with cytomegalic inclusion body disease in whom the brain was involved. The EEG findings are discussed. When repeated recordings were available variations occurred, apparently mirroring various phases in the course of the illness. The symptomatology, diagnostic problems and aetiology are discussed.