It is widely known that metformin reduces the levels of circulating pro-coagulant factors and improve fibrinolytic activity in type 2 diabetes when used in therapeutic doses. Potential alterations of coagulation have not been reported in patients with metformin intoxication. We evaluated certain components of the coagulation system in a patient with metformin intoxication upon admission and after recovery. Our results indicate that both the levels of coagulation proteins synthesized by the liver and the anti-coagulant activity decrease temporarily in metformin intoxication. Nevertheless, no change in the coagulation factors secreted by the endothelium were observed.