Autoimmune encephalitis should be excluded in unexplained encephalitis. A significant portion of autoimmune encephalitis in childhood is anti- NMDA encephalitis. However, neuroimaging and routine diagnostic tests are inadequate, diagnosis sholud be confirmed by the demonstration of autoantibodies. The treatment may be delay in this process. Extreme delta brush waves are unique electroencephalography pattern, seen in some of Anti-NMDA encephalitis, useful for early diagnosis. Extreme delta brush activity is associated with prolonged hospitalization and illness. Despite of these, the specificity and sensitivity of this pattern is not-known clearly. We present a five years old boy with the loss of consciousness, involuntary movements, intermittant generalized tonic clonic seizures and extreme delta brush activity in electroencephalography.