The authors report spontaneous thrombosis of a middle cerebral artery aneurysm in a patient receiving the anti-fibrinolytic agent, epsilon aminocaproic acid. Intense vasospasm and profound neurologic deficit accompanied the initial hemorrhage. Follow-up angiography two, four and ten weeks following the initial hemorrhage demonstrated occlusion of the aneurysm and progressive thrombosis of a middle cerebral artery branch despite the disappearance of vasospasm. The patient had a persistent hemiparesis.