In 1900 Klippel and Trenaunay defined a new entity characterized by cutaneous angioma associated with varices and hypertrophy of bone and soft tissues. The syndrome is present in the earliest years and becomes accentuated as the child grows. It typically affects one half of the body. We report two cases of Klippel-Trenaunay syndrome. The first patient presented with flaccid paraplegia. On T1-weighted MRI sequences a diffuse heterogeneous high-intensity signal was visible opposite the T8 and T9 vertebral bodies. Spinal cord angiography showed occlusion of the anterior spinal artery issued from Adamkiewicz's artery, suggesting thrombosis. Serum fibrinopeptide A level was very high and compatible with hypercoagulability. The second patient presented with left hemiplegia caused by a right superficial sylvian artery infarct, and carotid angiography showed an image of right internal carotid artery dissection. These two cases suggest that Klippel-Trenaunay syndrome includes a state of hypercoagulability facilitating the occurrence of arterial thrombotic accidents, and an abnormality of the arterial wall capable of determining spontaneous dissection. A study of arterial wall-dependent coagulation factors should establish a link between these two aetiological factors. All this argues in favor of a diffuse vascular pathology, which makes this syndrome close to phakomatoses.