Since the first description of encephalopathy associated with Hashimoto's thyroiditis in 1966, more than 100 cases of this entity called Hashimoto's encephalopathy or SREAT [steroid-responsive encephalopathy associated with auto-immune thyroiditis] have been reported. The two cases reported here illustrate different diagnostic criteria and offer the opportunity to discuss the many pathophysiological hypotheses based on particularly pertinent biological data, especially the activity of anti-TPO and anti-TG antibodies present in serum and cerebrospinal fluid and the recent discovery of anti-alpha-enolase antibody. Different treatment options are also discussed, in particular corticosteroid therapy.