Metformin is one of the commonly used drugs in type-2 diabetes mellitus. It reduces glucose levels by increasing insulin sensitivity, reducing hepatic glucose release and increasing muscle uptake. One of the serious complications associated with metformin use is lactic acidosis, and it is associated with high morbidity and mortality. This is more likely to happen in patients with renal failure due to reduced clearance. International guidelines recommend discontinuing metformin in advanced renal failure. We report a case of metformin-associated lactic acidosis in a patient with end-stage renal disease on peritoneal dialysis. The patient presented with severe lactic acidosis, which was successfully treated with hemodialysis.