Encephalitis is an inflammatory process that affects brain tissue. Encephalopathy implies cerebral dysfunction due to circulating toxins, poisons, abnormal metabolites or intrinsic biochemical disorders affecting neurons but without inflammatory response. Encephalitis is almost always accompanied by inflammation of the adjacent meninges, thus the term meningoencephalitis. Both entities may be caused by a wide variety of agents. Some of the causes are self-limiting, while others may rapidly lead to death or severe neurological damage. Diagnosis of encephalitis with absolute certainty is only possible by microscopic examination of brain tissue. Acute encephalitis is more common in children (more than 16 cases per 100,000 patient years) than in adults (between 3.5 and 7.4 cases per 100,000 patient years). In the United States, about 1000-2000 cases of viral encephalitis are reported to the Center for Disease Control, Atlanta annually. Its incidence in India is not known.