Hashimoto encephalopathy is a neurological disorder associated with autoimmune thyroiditis. Two forms may be identified: a vasculitic type with stroke like episodes and a diffuse progressive type with dementia. Response to steroids is usually favorable. Previous cases were characterized by a relapsing or progressive encephalopathy in association with high titers of antithyroid antibodies and euthyroidism/mild hypothyroidism. Rare cases with Graves disease were also described. A few cases were associated with fever. We describe a 52-year-old man with Graves disease and high antithyroid peroxidase antibody titer in whom presence of fever led to the confusion in differential diagnosis. Our patient had a subacute progressive neuropsychiatric disorder. This history was complicated by the development of an acute confusional state, fever, tremulousness and extrapyramidal. motor rigidity. At the time of admission, serum thyroid hormone concentrations were T3: 0.6 ng/mL (N: 0.5-1.8 ng/mL), T4: 9.1 mug/dL (N: 4.8-12.8 mud/dL), free T4: 27.9 pmol/L (N: 10-25 pmol/L) and TSH was 0.007 muU/mL (N: 0.4-4.0 muU/mL). Thyroid storm could not be excluded and the patient underwent plasmapheresis after which the clinical pica lure was significantly improved. However cognitive impairment persisted. This disorder should be considered in patients with autoimmune thyroid disease and unexplained acute/subacute neurologic deterioration.