Hashimoto encephalopathy (HE) is a rare steroid-responsive encephalopathy associated with elevated antithyroid antibodies and is a well recognised complication of autoimmune thyroid disease. The clinical picture is pleomorphic, presenting with variable symptoms like coma, seizures, neuropsychiatric changes (impairment of cognitive functions, behavioural and mood disturbances, hallucinations) or focal neurological deficits. HE is mainly diagnosed in adults, but also a rare differential diagnosis of encephalopathy or epilepsy in children. The diagnosis is often overlooked at presentation but is crucial as it is a treatable disease. We report on the youngest patient described up to now presenting with progressive epilepsy resistant to anticonvulsive treatment and unclear encephalopathy related to Hashimoto thyroiditis.