It has been stated that chest radiographic features of aortic dissection are a contraindication to intravenous thrombolysis in patients with suspected acute myocardial infarction. Excluding aortic dissection could significantly delay such treatment in patients who would benefit from thrombolysis. Initial chest radiographs of 18 patients with acute aortic dissection and 25 patients with acute myocardial infarction were evaluated. The radiographs were studied by two experienced radiologists for signs of aortic dissection. No radiographic signs or combinations of signs accurately distinguished aortic dissection from myocardial infarction. Patients with chest radiographic signs suggesting aortic dissection but with clinical features suggesting myocardial infarction should not be denied the benefits of immediate intravenous thrombolysis.