The management of patients with acute aortic dissection requires a rapid diagnosis and precise information about the localization and extent of the dissection. Four imaging techniques are currently available to diagnose aortic dissection: aortography; contrast-enhanced computerized tomography (CECT); magnetic resonance imaging (MRI); and transesophageal echocardiography (TEE). All of these techniques have their specific advantages and inherent limitations. Recent studies have demonstrated that MRI may best provide a comprehensive and detailed evaluation of the thoracic aorta, therefore proposing this technique as a "new gold standard" in the diagnosis of acute aortic dissection. TEE, however, may be the best alternative technique, as it combines high sensitivity and specificity with high practicality. The practicality is particularly important in hemodynamically unstable patients in whom a rapid bedside imaging modality is required. CECT might be necessary in selected cases in whom TEE fails to provide a definite diagnosis. Aortography may be necessary in patients in whom clinical signs are suggestive of organ ischemia and in whom coronary anatomy needs to be delineated before operation. (ECHOCARDIOGRAPHY, Volume 13, March 1996)