Steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT), also known as Hashimoto encephalopathy, represents a rare disorder of presumed autoimmune origins that can be diagnosed when a protean variety of psychiatric symptoms are present in association with elevated titers of anti-thyroid antibodies. Symptoms can have a rapid and complete remission with corticosteroid treatment. A 19-year-old girl, with clinical history of Basedow-Graves disease, has been admitted to our department after presenting acute psychiatric symptomatology. Clinical and serological findings were used to formulate the diagnosis of SREAT, confirmed by subsequent positive response to corticosteroid treatment. SREAT can mimic an acute psychiatric symptomatology, thus it seems extremely relevant for psychiatrists to consider this syndrome in differential diagnosis algorithm, especially in those patients presenting a history of autoimmune thyroid disorder, in order to ensure adequate diagnosis and treatment.