BACKGROUND In several studies, prolongation of the corrected QT (QTc) interval has been associated with an increased risk of cardiac events. However, data on race and gender variation in the QTc and its associated risk of death are lacking. METHODS We prospectively followed 19,252 subjects who underwent cardiac catheterization and had at least 1 native coronary artery stenosis ≥75%. Automated QTc measurements were obtained from a baseline electrocardiogram. RESULTS The mean age of the population was 62.4 years, with 35% being female and 20% being black. The QTc varied by gender and race (417.9 ± 34.4 ms in men and 433.4 ± 33.6 ms in women, 422.1 ± 34.3 ms in whites and 428.1 ± 36.9 ms in blacks; P < .0001 for both). Risk factors most strongly associated with a prolonged QTc were lower ejection fraction, higher diastolic blood pressure, history of myocardial infarction, and lower glomerular filtration rate. Black race and female gender were also independently associated with a prolonged QTc, after adjustment for cardiac risk factors. Moreover, there was an independent association between QTc and all-cause mortality (hazard ratio 1.037 per 10-ms increase, P < .0001). The increased mortality risk associated with a 10-ms increase in the QTc interval was significantly greater for men compared with women (4.6% vs 2.4%, P = .004) and slightly greater for blacks compared with other races (5.0% vs 3.3%, P = .057). CONCLUSIONS Among patients with coronary artery disease, QTc prolongation is independently associated with all-cause mortality. The increased mortality risk is higher for men than for women, with a trend toward higher mortality in blacks.