A common clinical conundrum faces all U.S. practitioners treating patients with type 2 diabetes. Today’s U.S. Food and Drug Administration prescribing guidelines for metformin contraindicate its use in men and women with serum creatinine concentrations ≥1.5 and ≥1.4 mg/dL (≥132 and ≥123 µmol/L), respectively. In a patient tolerating and controlled with this medication, should it automatically be discontinued as the creatinine rises beyond these cut points over time? Stopping metformin often results in poorly controlled glycemia and/or the need for other agents with their own adverse-effect profiles. Moreover, is the now widespread use of estimated glomerular filtration rate (eGFR) in lieu of serum creatinine levels creating even more confusion, especially in those with abnormalities in one but not the other indirect measure of renal function? Indeed, more than a decade and a half after metformin became available in the U.S., debate continues over the best approach in these settings. How many patients are unable to receive this medication on the basis of guidelines which, although well intentioned, are somewhat arbitrary and outdated based on modern assessments of renal status?