Acute disseminated encephalomyelitis (ADEM) is an immune mediated central nervous system disorder. It is characterized by an inflammation response and demyelination of the Central nervous system (CNS), which influences the white matter of brain and spinal cord. ADEM can appear at any age but is more common in children with good prognosis and rare in middle and elderly age group and due to non-reported cases in literature their outcomes are unknown. ADEM seems more in winter and spring season, with male to female proportion of 3:1, in all parts of world in all ethnic gatherings. ADEM is monophasic disease with beneficial long time prognosis in children. The condition generally occur and accelerated by a viral disease mainly exanthemata’s disease including measles, influenza, EpsteinBarr virus, rubella, hepatitis, varicella or inoculation e.g., rabies, small pox, polio or measles vaccines. The hallmark of pathogenesis of post infectious encephalomyelitis is zones of perivenous demyelination and penetration of lymphocytes and macrophages. The current confirmation proposes that ADEM comes about because of a transient immune system reaction against myelin or different auto antigens, potentially, by means of molecular mimicry or by non-specific actuation of an auto reactive T cell clone. Peptides from microbial proteins that have adequate basic similitude with the host’s self-peptides can enact auto reactive T cells; this mechanism is called molecular mimicry.