Lactic acidosis is a rare but severe complication in patients with type 2 diabetes treated with metformin. Patients with lactic acidosis show commonly signs of shock, tissue hypoxia, acute hepatic or renal failure and the link between metformin therapy and lactic acidosis may be coincidental, associated or causal. Excessive plasma metformin concentrations show that lactic acidosis is due to a toxicological mechanism. We report a case of severe multiorganic failure in a subject after treatment with high doses of metformin.