Segmental arterial mediolysis is a vascular disease of putative vasospastic origin that causes massive hemorrhages. Although once considered rare, awareness of this disease has resulted in increased reports in the pathology and radiology literature. Despite this, uncertainties concerning pathologic and radiologic correlations, the course of this disease, and aspects of its prognosis exist. This article addresses these issues. Thirteen radiologic reports of segmental arterial mediolysis are analyzed, and slides of 25 cases of segmental arterial mediolysis are searched for lesions analogous to the radiologic findings. Six angiographic presentations are identified: (a) arterial dilatation, (b) single aneurysm, (c) multiple aneurysms, (d) dissecting hematomas, (e) arterial stenosis, and (f) arterial occlusions. Pathologic correlations reveal that lytic loss of medial muscle causes arterial dilatation, dilated arterial gaps form aneurysms, dissections develop at arterial-medial gap junctions or from reparative granulation tissue and reparative alterations, and thrombi cause stenosis and occlusions. The most common radiologic findings at onset are aneurysms, arterial dilatation, and occlusions, while dissections and stenotic lesions often are delayed. These images correlate with the histologic evolution of segmental arterial mediolysis. Segmental arterial mediolysis is an acute limited disease. Sequelae recognized radiologically include aneurysms, dissecting hematomas, arterial stenosis, and occlusions. Generally, these persist, become smaller, or resolve, but symptomatic dissections with delayed onset occur. Sequelae of subclinical forms of segmental arterial mediolysis may cause isolated idiopathic aneurysms or may evolve into arterial lesions indistinguishable from fibromuscular dysplasia.