A 43-year-old female, who had been treated for systemic lupus erythematosus (SLE), presented with a subarachnoid hemorrhage (SAH) induced by rupture of cortical venous thrombosis, and be followed by medial medullary infarction during the acute stage of the SAH. The patient initially manifested a SAH. Angiography demonstrated no evidence of any aneurysms or arteriovenous malformations, but revealed cortical venous thrombosis. She suddenly developed left hemiplegia caused by medial medullary infarction on the 6th day. An active anticoagulant therapy was thought to be inappropriate because of initial symptoms as a hemorrhage. Since she had been accompanied by the medullary infarction, then, initially started by antiplatelet therapy. After the confirmation of no saccular or dissecting aneurysms with 2nd angiography, her treatment could be changed to anticoagulant therapy. Because of the sustained negative reactions of anti-cardiolipin beta 2 glycoprotein I antibody and lupus anticoagulant during the course of SLE, the definite diagnosis of antiphospholipid syndrome (APS) could not be made. However, this case is pathogenically thought to be cerebrovascular disease based upon APS, considering that this syndrome may be related to various antigen/antibody systems.