Cryptogenic epilepsy is an epilepsy of presumed symptomatic nature but the cause has not been identified. It account for at least 40% of adult-onset epilepsy. Autoimmune encephalitis including classic paraneoplastic syndrome and autoimmune synaptic encephalitis is a new category of immune-mediated disorders which often has favorable outcome. Recent studies reported that immunotherapy improves seizure outcome in medically intractable epilepsy patients with clinical and serological evidence of an autoimmune basis. Neural autoantibodies were detected in 22% of epilepsy due to unknown cause in a study, mostly from the antiepileptic drug(AED)-resistant epilepsy group. Of the patients who received immunotherapy, 75% archived >50% reduction in seizure frequency.