BACKGROUND Metformin-associated lactic acidosis (MALA) is a relatively rare adverse effect of metformin therapy. It usually occurs in patients with metformin overdose or in those with underlying acute and/or chronic conditions resulting in impaired lactate metabolism. Among these, patients with acute kidney injury, heart failure, sepsis, and cirrhosis are the most vulnerable to MALA, even in the setting of appropriate therapy. The most common symptoms of MALA include nausea, vomiting, diarrhea, encephalopathy, hypothermia, respiratory failure, and hypotension. Blindness is a dramatic symptom that has been rarely reported with MALA. CASE REPORT We report a case of 78-year-old woman with history of type 2 diabetes mellitus with nephropathy for which she was treated with metformin and insulin. She developed nausea, non-bloody emesis, and watery diarrhea, which led to dehydration, anion gap metabolic acidosis due to hyperlactatemia, and acute kidney injury (AKI). She was hospitalized for i.v. hydration and further management when she suddenly developed blindness. The diagnostic work-up ruled out central causes and her symptoms resolved briefly after continuous renal replacement therapy (CRRT) was initiated, confirming the diagnosis of MALA. CONCLUSIONS By reporting this case, we wish to increase awareness about MALA symptoms, its diagnosis, and the importance of early recognition and initiation of treatment among clinicians involved in the care of patients with chronic kidney disease (CKD) who take metformin for diabetes mellitus. Although rare, this metformin adverse effect can present dramatically and can be distressing for both patient and treating team.