This study examines the prognostic implications of normal exercise tomographic thallium images in medically treated patients with angiographic evidence of coronary artery disease (CAD). There were 97 patients aged 60 +/- 10 years; 52 had 1-, 30 had 2-, and 15 had 3-vessel CAD (> or = 50% diameter stenosis). The exercise test was submaximal in 51 patients (53%); ST-segment depression during exercise occurred in 20 patients (21%), and angina during exercise occurred in 23 patients (24%). Most patients (71%) were receiving antianginal therapy. During a mean follow-up of 32 months, only 3 patients had cardiac events: 2 died of cardiac causes and 1 had nonfatal myocardial infarction (event rate 1.1%/year). None of those 3 patients had positive ST response during exercise. Thus, medically treated patients with CAD (including those with multivessel CAD) have a benign prognosis in the presence of normal exercise thallium images. These results have important implications in patient management and cost of health delivery.