Diabetic patients undergoing coronary interventions have worse clinical and angiographic outcomes than do patients without diabetes. Metformin, an insulin sensitizer, may decrease the occurrence of these outcomes. Diabetic patients in the Prevention of Restenosis with Tranilast and its Outcomes Trial were identified through their medical records (n = 2,772). In this trial, 1,110 diabetic patients received nonsensitizer therapy (insulin and/or sulfonylureas) and 887 received sensitizer therapy (metformin with or without additional therapy). Logistic regression was used to obtain odds ratios (ORs) (sensitizer vs nonsensitizer therapy) of any clinical event (death, myocardial infarction, or ischemia-driven target vessel revascularization) and adjusted for multiple risk factors. Multivariate analysis showed no effect of lesion characteristics on clinical outcomes. Compared with patients on nonsensitizer therapy, those on sensitizer therapy showed an adjusted OR of 0.72 (95% confidence interval [CI] 0.57 to 0.91, p = 0.005) for any clinical event. The differences between the nonsensitizer therapy group and the sensitizer group were attributable mainly to decreased rates of death (OR 0.39, 95% CI 0.19 to 0.77, p = 0.007) and myocardial infarction (OR 0.31, 95% CI 0.15 to 0.66, p = 0.002). In our retrospective analysis, use of metformin in diabetics undergoing coronary interventions appeared to decrease adverse clinical events, especially death and myocardial infarction, compared with diabetic patients treated with nonsensitizer therapy.