Epidemic encephalitis is an infectious disease of as yet unknown etiology, but of a well-established pathology. The cerebro-spinal nervous system, especially the brain, bears the brunt of the infection. The anatomical picture is characterized by marked congestion and edema, infiltration of the Virchow-Robin lymph spaces by lymphocytes and plasma cells; distension and occasional rupture of vessels resulting in hemorrhage; moderate cloudy swelling of the ganglion cells with chromatolysis, satillitosis and occasionally neurononphagy; and moderate neuroglia reaction. The pathological process is a changing and progressive one. The mental picture results from the action of the encephalitic virus and inflammatory exudates upon the nerve tissue. The clinical reaction, therefore, may be that of an acute organic psychosis in which there is a constant changing of symptoms. Occasionally the toxemia may bring to the surface deeply rooted mental conflicts, adding a psychogenic coloring to the presenting symptoms. The encephalitic virus may first attack those parts of the brain that control the highest psychic processes (frontal lobes) and may produce a psychosis as the earliest clinical manifestation. The early recognition of these cases are of tremendous medical and sociological importance.