The pandemic of von Economo's disease which began in January 1917 preceded that of influenza of 1918-1919 by more than a year. Though it has been customary to link the two it seems unlikely that the latter was responsible for the former as has been proposed. It has been assumed that von Economo's disease (ED) was caused by a virus; but in fact the etiology is in question as no virus has yet been transmitted to experimental animals or cells in culture. However, the presence of oligoclonal IgG bands in the CSF of suspected cases and the finding of chronic active lesions in the brain tissue at autopsy suggests a viral etiology. Occasional, sporadic presumed cases of the disease have been reported within the last 25 years. Encephalitides due to established neurotropic viruses or to other viruses that may on occasion invade the CNS only rarely produce parkinsonism, and when they do it differs from that seen in ED. The present report reviews the overall concept of a viral etiology of Parkinson's disease with particular reference to von Economo's disease.