An unusual case of cavernous hemangioma of the superior mediastinum in a 38-year-old male is presented. Mediastinal hemangiomas occur more often in children and are usually localized in the anterior-superior compartment in all age groups. Slow expansile growth, lack of infiltration of adjacent structures and microscopically mature cellular elements clearly marked the benign nature of the lesion. Vascular mesenchymal tumors in this location must be approached with caution because of the risks of hemorrhage or local infiltration of vital structures. Electron microscopy revealed active endothelial cells, smooth muscle cells, and intercellular matrix components suggestive of smooth muscle cell origin. Computerized tomography delineated the lesion clearly and demonstrated identical densities for the mass and adjacent blood vessels.