Five patients with recent spontaneous or post-traumatic dissection of the internal carotid artery (ICA) were explored by magnetic resonance imaging (MRI), using T1-weighted axial sections in all cases. In four patients examined during the subacute phase (after 7 days) the diagnosis of ICA dissection was strongly suspected on the association of a very high intensity signal produced by the parietal haematoma with a contiguous signal void area corresponding to the lumen of the ICA. A control MRI examination performed in two patients 2 months after the onset of dissection showed that it had regressed and that the carotid arteries were patent, which was confirmed by angiography. In the fifth patient MRI provided evidence for the evolution of a post-traumatic dissection towards thrombosis. The MRI image of carotid dissection at the subacute phase seems to be characteristic. MRI is also useful to follow up dissections under treatment and to postpone angiography. The latter, however, remains necessary to investigate for associated arterial dysplasia and to evaluate the sequelae of dissection.