Patients scheduled to undergo ambulatory surgery are usually made non per os (NPO) at midnight on the day prior to surgery. In the case of patients with type 2 diabetic mellitus (DM) on treatment with oral hypoglycemic agent (OHA), patients are instructed to temporarily discontinue treatment on the day prior to surgery. This advice is based on the concern for intraoperative and postoperative hypoglycemia in this group of patients. Metformin , a dimethylbiguanide, is widely used as an oral antihyperglycemic drug in the long term treatment of type 2 DM. This instruction to withhold treatment may be imprudent given that metformin by virtue of its mechanism of action does not cause hypoglycemia. Another concern often cited as a reason to withhold metformin is the reported adverse effect of lactic acidosis. However, a recent metanalysis by the Cochrane group found no cases of fatal or nonfatal lactic acidosis in 70,490 patient-years of metformin use, or in 55,451 patient-years for those not on metformin. Furthermore, discontinuing OHA treatment can result in disruption of established glycemic control and intraoperative and postoperative hyperglycemia all of which can be deleterious to the patient.