We studied 455 patients (mean age, 51 years) in whom exercise thallium 201 scintigrams performed for suspected coronary artery disease were normal. Of those, 322 (71%) had typical or atypical angina pectoris and 68% achieved 85% or more maximal predicted heart rate. The exercise ECGs were abnormal in 68 patients (15%), normal in 229 (50%), and inconclusive in 158 (35%). Ventricular arrhythmias occurred during exercise in 194 patients (43%). After a mean follow-up period of 14 months, four patients had had cardiac events, sudden cardiac death in one and nonfatal myocardial infarctions in three. None of the four patients had abnormal exercise ECGs. Two had typical and two had atypical angina pectoris. Normal exercise thallium 201 images identify patients at a low risk for future cardiac events (0.8% per year), patients with abnormal exercise ECGs but normal thallium images have good prognoses, and exercise thallium 201 imaging is a better prognostic predictor than treadmill exercise testing alone, because of the high incidence of inconclusive exercise ECGs and the good prognosis in patients with abnormal exercise ECGs.