Spontaneous thoracic aortic dissection carries a high mortality despite progress in diagnosis and treatment. Early and accurate diagnosis is paramount and dependent on clinical and diagnostic imaging skills. A retrospective review of 55 consecutive patients referred with suspected thoracic aortic dissection to a medical cardiology department was performed. Clinical follow up was complete to November 1995. Median age was 68 years (range 30-93), with 37 males, 18 females. Presenting complaints included interscapular chest pain in 23 (42 per cent), neurological deficit in 2 (4 per cent), and limb ischaemia in 8 (15 per cent). On examination 34 (62 per cent) patients had hypertension, 5 (9 per cent) a pulse deficit and 10 (18 per cent) aortic incompetence. Electrocardiography confirmed myocardial infarction in 1. Chest X-ray showed a widened mediastinum in 37 (67 per cent) patients. Dissection was confirmed in 35 (64 per cent) patients (13-DeBakey Type I, 6-Type II, 14-Type III); 10 had nondissecting aneurysm. Contrast aortography was equally sensitive (84 per cent) and more specific (100 per cent vs 80 per cent) than computed tomography for detection of dissection. Surgical repair was performed on 24 patients with concomitant coronary artery bypass grafting in 6. At follow up 33 patients were alive. Clinical diagnosis of thoracic aortic dissection or aneurysm may be difficult. Frequently more than one imaging modality may be required in order to provide all of the necessary information for optimal patient management.