Hashimoto encephalopathy is a steroid-responsive encephalopathy associated with elevated blood concentrations of antithyroid antibodies. The patients are usually euthyroid or mildly hypothyroid. The clinical picture is pleomorphic, presenting with variable symptoms ranging from behavioral and cognitive changes, myoclonus, seizures, pyramidal tract dysfunction, involuntary movements, and cerebellar signs to psychosis and coma, with relapsing and progressive course. The diagnosis is often overlooked at presentation but is crucial, given that this is a treatable disease. Described here, with a literature review, is the youngest patient reported to date with Hashimoto encephalopathy.