Hashimoto's encephalopathy is a severe and rather infrequent clinical condition initially described in patients suffering from chronic lymphocytic thyroiditis. Its origin is still controversial but it can be agreed to have an autoimmune etiology. In fact, its most characteristic finding is the high titre of antithyroid antibodies, especially antimicrosomal. We describe three cases of Hashimoto's encephalopathy and establish a relationship between the clinical status, the antithyroid antibody levels and its response to corticosteroid treatment. There was an excellent response to corticosteroid treatment in all three cases. Interestingly, one case was associated with Graves' disease. Given this, and after the review of the literature, we believe that the term 'encephalopathy associated to autoimmune thyroid disease' could be more appropriate to define this entity. Finally, we suggest that autoimmune thyroid encephalopathy must be suspected in the face of unaccounted acute or subacute encephalopathy with high levels of antithyroid antibodies.