We describe a patient with a clinical picture characterized by subacute onset of confusion, myoclonus, tremor and generalized convulsive seizures with a relapsing course, which was attributed to Hashimoto's encephalopathy. EEG and MRI were diffusely abnormal. High titers of antithyroid antibodies were detected in her serum. She responded well to corticosteroids and her condition remained good during a one-year follow-up.