Autoimmune encephalitis is a severe inflammatory disorder of the brain with diverse causes and a complex differential diagnosis. Recent advances in the past decade have led to the identification of new syndromes and biological markers of limbic encephalitis, the commonest presentation of autoimmune encephalitis. The successful use of serum and intrathecal antibodies to diagnose affected patients has resulted in few biopsy and postmortem examinations. In those available, there can be variable infiltrating inflammatory T cells with cytotoxic granules in close apposition to neurons, consistent with an inflammatory autoimmune basis, but true vasculitis is rarely seen. The exception is Hashimoto encephalopathy.