A 51-year-old Korean man with end-stage renal disease and who was on intermittent hemodialysis was admitted with progressive dysarthria, gait disturbance, and myoclonus. The liver function tests and the electrolyte and arterial gas analyses were normal. The Magnetic resonance imaging scan showed a diffuse symmetric high signal intensity in the basal ganglia on the T2-weighted image. After a thorough history taking, we knew that he had been treated with metformin for 3 months at other hospital without our hospitals staff's knowledge. After stopping the metformin, the patient's neurologic signs and symptoms disappeared and the Magnetic resonance imaging findings after 20 days were markedly improved.