OBJECTIVES: Type II diabetes mellitus (T2DM) is associated with an increased risk of pancreatic adenocarcinoma (PAC). Epidemiological evidence indicates that metformin use, a biguanide used as a first-line treatment for diabetes, may decrease the risk of PAC. Our objective was to evaluate metformin chemoprevention in T2DM patients with respect to life expectancy, PAC incidence and mortality, and net difference in quality-adjusted life years (QALYs). METHODS: A previously published state-transition model of PAC was revised to reflect increased all-cause mortality and risk of progression for pancreatic cancer in patients with diabetes. A hypothetical cohort of patients with T2DM for two years or more were treated with metformin starting at age 50 (base case). The primary endpoint was net gain in life expectancy (LE) compared to no treatment. Secondary endpoints included the number needed to treat (NNT) to prevent one PAC incidence, and NNT to prevent one PAC death, and change in QALYs. Sensitivity analyses were performed on key model inputs, including the decreased risk for PAC incidence on metformin, adherence rates to treatment, and quality of life (QoL) changes due to GI side effects. RESULTS: Treatment with metformin resulted in an overall LE gain of 0.01476 years for diabetic patients, a NNT of 641 to prevent one PAC incidence, and a NNT of 825 to prevent one PAC death, but a decrease in -0.01173 QALYs. The results were sensitive to the decreased PAC risk from taking metformin, adherence rate to the treatment, and disutility of taking metformin.  CONCLUSIONS: Metformin led to an increase in LE gained because of reduced cancer deaths but a decrease in QALYs as a result of side effects. Patients may want to weigh both the possible chemopreventive benefits and the possible impact on QoL in treatment decisions.