Abnormalities in plasma glucose below the "diabetic range" of glycemia are associated with increased cardiovascular morbidity and mortality in patients without diabetes mellitus. The purpose of this study was to investigate the relation between ambient glycemic levels as measured by hemoglobin A1c and outcome after elective percutaneous coronary intervention (PCI). Baseline laboratory studies, including hemoglobin A1c, were drawn in 500 consecutive patients before elective PCI. Nondiabetic patients were defined as those without a history of diet or pharmacologically controlled diabetes mellitus and a hemoglobin A1c level <7.0%. Of the 500 patients studied, 291 (59%) were nondiabetic patients. Abnormal hemoglobin A1c levels (6% to 7%) were found in 30% of nondiabetic patients. Nondiabetic patients with an abnormal hemoglobin A1c level had a significantly higher rate of major adverse cardiac events (33% vs 22%, p = 0.04), target vessel revascularization (31% vs 19%, p = 0.02), and cardiovascular mortality (4.6% vs 0.5%, p = 0.03) compared with nondiabetic patients with hemoglobin A1c levels <6%. Multivariate analysis disclosed that a hemoglobin A1c level of 6% to 7% was a significant independent predictor of major adverse cardiac events, target vessel revascularization, and cardiovascular mortality 12 months after PCI in nondiabetic patients. These data demonstrate that an abnormal hemoglobin A1c level may have prognostic significance in nondiabetic patients who undergo PCI.