Two cases of cerebral transmural angiitis and ruptured aneurysm in patients with established systemic lupus erythematosus are presented. A 22-year-old woman with a 4-year history of systemic lupus erythematosus was found to have a ruptured cerebral aneurysm at the trifurcation of the middle cerebral artery. She died 10 days after admission because of the brain swelling. Necropsy showed remarkable brain edema and focal transmural angiitis at the site of the ruptured aneurysm. Another 29-year-old woman with a 3-year history of systemic lupus erythematosus had an acute subdural hematoma resulting from a ruptured aneurysm of the right anterior cerebral artery. She was surgically treated. The ruptured aneurysm was resected and examined histologically. The transmural angiitis was demonstrated. This report describes two radiographically and pathologically confirmed cases of central nervous system lupus producing focal angiitis of a cerebral artery with secondary aneurysm formation.