Hyperglycemia commonly is observed as part of the hypermetabolic response to severe burn injury. In routine burn care, physicians use interventions to address and reduce the complications of this stress-induced hyperglycemia. Metformin (1,1-dimethylbiguanide), an orally administered hyperglycemic medication, has been used previously to modulate the stress-induced hyperglycemic response in nondiabetic burn patients. The use of this medication in nonburn diabetic patients has been associated with the development of lactic acidosis. We present an acute burn patient who developed lactic acidosis while receiving metformin for management of his diabetes.