<p>Metformin is a major drug for the treatment of type 2 diabetes mellitus; however, its use is not recommended in dialysis patients due to the risk of lactic acidosis. Consequently, there are very few reports of metformin-associated lactic acidosis (MALA) or metformin-associated encephalopathy in dialysis patients. We report a case of a 67-year-old man undergoing maintenance hemodialysis who was admitted to our hospital with impaired consciousness. Blood tests revealed marked hypoglycemia (blood glucose level of 18 mg/dL) in addition to severe metabolic acidosis and lactic acidosis (pH 6.989, HCO3- 5.8 mmol/L, and lactate 10.7 mmol/L). The patient had a history of metformin use, and was diagnosed with MALA. We immediately initiated glucose correction and emergency hemodialysis. On the same day, magnetic resonance imaging (MRI) showed symmetrical swelling in the bilateral basal ganglia, with low signal intensity on T1-weighted images and high signal intensity on T2-weighted and fluid-attenuated inversion recovery images, leading to a diagnosis of metformin-associated encephalopathy. The patient’s condition improved with frequent dialysis sessions, and subsequent MRI showed improvement in the lesions. The patient was discharged on the 17th day, after confirming recovery to the pre-admission level. The present case reinforces the recommendation that metformin should not be prescribed to patients undergoing dialysis.</p>