Resting 12-lead electrocardiographic records from 849 patients who underwent coronary cineangiographic studies were reviewed for U wave negativity without knowledge of the clinical data or angiographic results. In order to evaluate U wave negativity as an independent electrocardiographic sign, patients with significant Q waves in the anterior leads were excluded from the final data analysis leaving 760 patients. Twenty-seven patients had U wave negativity in leads I, aVL or V4 through V6. For the study population, the prevalence of coronary artery disease was 64 percent (484 or 760); the prevalence of significant left anterior descending or left main coronary artery stenosis was 46 percent (350 of 760); and the prevalence of angiographic left ventricular dysfunction was 41 percent (309 of 754). Among 27 patients with resting U wave negativity the prevalence of coronary artery disease was 89 percent (24 of 27); the prevalence of left anterior descending or left main disease was 89 percent (24 of 27); and the prevalence of angiographic left ventricular dysfunction was 80 percent (20 of 25). Among patients selected for coronary cineangiographic study, U wave negativity was a significant predictor (p < 0.001) of greater than or equal to 75 percent stenosis of the left anterior descending or left main coronary artery and of left ventricular dysfunction (p < 0.001).