© 2015 American College of Physicians. Background: Prediabetes affects 1 in 3 Americans. Both intensive lifestyle intervention and metformin can prevent or delay progression to diabetes. Over the past decade, lifestyle interventions have been translated across various settings, but little is known about the translation of evidence surrounding metformin use. Objective: To examine metformin prescription for diabetes prevention and patient characteristics that may affect metformin prescription. Design: Retrospective cohort analysis over a 3-year period. Setting: Employer groups that purchased health plans from the nation's largest private insurer. Participants: A national sample of 17 352 working-age adults with prediabetes insured for 3 continuous years between 2010 and 2012. Measurements: Percentage of health plan enrollees with prediabetes who were prescribed metformin. Results: Only 3.7% of patients with prediabetes were prescribed metformin over the 3-year study window. After adjustment for age, income, and education, the predicted probability of metformin prescription was almost 2 times higher among women and obese patients and more than 1.5 times higher among patients with 2 or more comorbid conditions. Limitation: Missing data on lifestyle interventions, possible misclassification of prediabetes and metformin use, and inability to define eligible patients exactly as defined in the American Diabetes Association guidelines. Conclusion: Evidence shows that metformin is rarely prescribed for diabetes prevention in working-age adults. Future studies are needed to understand potential barriers to wider adoption of this safe, tolerable, evidence-based, and cost-effective prediabetes therapy. Primary Funding Source: Centers for Disease Control and Prevention (Division of Diabetes Translation) and the National Institute of Diabetes and Digestive and Kidney Diseases.