We describe a patient with established systemic lupus erythematosus (SLE) in whom an intracerebral hemorrhage developed secondary to a ruptured aneurysm of the lenticulostriate artery (LSA). A 24-year-old woman with a four-year history of SLE was admitted to the department of internal medicine of Iwate Medical University for the treatment of lupus nephritis in 1985. She suddenly complained of severe headache and nausea, and soon lost consciousness. The computed tomographic scan revealed intracerebral hemorrhage in the left front-temporal region and subarachnoid hemorrhage. Left common carotid angiography demonstrated a 3 X 3 mm aneurysm of the LSA and displacement of other LSAs and anterior cerebral artery. The incidence of intracerebral hemorrhage in SLE was about ten percent in the reported central nervous system SLE, and it seemed that the prognosis of SLE with intracerebral hemorrhage was poor. The mechanisms of the intracerebral hemorrhage and the aneurysmal formation in SLE seemed to be due to lupus angiitis, but without clinical, radiologic and pathologic correlation. In operation, a ruptured aneurysm without neck was found in LSA and extirpated. In the pathological study, there was transmural angiitis, which fibrinoid necrosis, elastic tissue disruption and infiltration of inflammatory cells were found. Inflammatory cells were chiefly lymphohistiocytic with some polymorphonuclear leukocytes. It seemed that pathologic studies confirmed transmural angiitis with secondary aneurysm formation.