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Evaluation of patients with recent onset of progressive cognitive and behavioral problems can be challenging. Psychiatric disorders, metabolic derangements, toxins and infections are generally considered in the differential diagnosis along with prion disorders (Creutzfeldt-Jakob disease) and rapidly progressive degenerative dementias. Some subacute encephalopathies are caused by autoimmune or inflammatory mechanisms, recognized by the association with autoantibody markers and/or clear response to immunomodulatory treatment. This review describes the clinical features of these potentially reversible autoimmune encephalopathies.Morvan syndrome, paraneoplastic limbic encephalitis (PLE), and nonparaneoplastic autoimmune limbic encephalitis have characteristic clinical and serological features. Limbic encephalitis is characterized by short-term memory impairment, complex partial temporal lobe seizures and psychiatric symptoms. Signal abnormalities in the mesial temporal lobes without contrast enhancement are the typical MRI findings. Morvan syndrome presents with behavioral changes, hallucinations, severe insomnia, autonomic hyperactivity and neuromyotonia (spontaneous muscle activity). Corticosteroid-responsive encephalopathy associated with evidence of thyroid autoimmunity (sometimes called Hashimoto encephalopathy) has a broad range of clinical presentation. Cognitive impairment with tremor, seizures, stroke-like events (including transient aphasia) and normal thyroid hormone levels is a common scenario. In the absence of diagnostic serological findings, clinical improvement with corticosteroids may be the only evidence of autoimmune encephalopathy.Autoimmune encephalopathies are an important cause of rapidly progressive cognitive and behavioral decline that probably remain under recognized. Electroencephalography, brain MRI, cerebrospinal fluid examination and serological tests are useful diagnostic tools. With increased clinical suspicion, these diseases may be diagnosed and treated successfully.