MRI has become the reference technique for the diagnosis and assessment of thoracic aortic aneurysms and subacute or chronic aortic dissections, and in the postoperative surveillance of the thoracic aorta. Several MRI techniques can now be used to investigate the thoracic aorta. The technique most widely used at the present time is Spin Echo imaging, which allows a multi-plane morphological approach to the thoracic aorta. It is often completed by a dynamic gradient echo sequence (cine-MRI) and, more recently, by ultra-rapid sequences (Turbo-Flash) following the injection of contrast agent. Phase-coding has also been proposed for the various intraluminal velocities. In the emergency situation, the examination of choice is less clearly defined due to the development of new techniques (transoesophageal ultrasonography, spiral computed tomography, MRI). The diagnostic strategy depends on the patient's clinical state, the respective advantages and limitations of each technique and the human and material resources available.