A 49 year old caucasian female with Hashimoto thyroiditis, developed during two years a neurological disorder with tonic-clonic and myoclonic seizures and confusional states. Some attacks were followed by a transient postictal aphasia. Some parallelism was noted between the clinical state and TSH levels. Neurological events disappeared with the normalisation of thyroïd functions. This association of Hashimoto thyroiditis and myoclonic encephalopathy has been rarely published. Pathogenesis could be double. Focal signs could be due to an auto-immune mechanism, perhaps through a vasculitis. A non-endocrine central action could explain diffuse signs: tonic-clonic seizures, myoclonus and confusional episodes.