We reviewed the medical records and autopsy reports of 50 patients with systemic lupus erythematosus to determine the clinical and neuropathological features of this disease. Neuropsychiatric disturbances were found in the majority (74%) of the patients, occurring as psychiatric illness only (5 patients), neurological idsorders only (15 patients), and both together (17 patients). Central nervous system (CNS) lesions were present in half the patients; embolic brain infarcts (10 patients) and CNS infections (8 patients) were the most common. Cardiac sources of emboli were Libman-Sacks endocarditis (5 patients), chronic valvulitis (2 patients), and left side of heart mural thrombus (2 patients). There was no evidence of active CNS vasculitis. Clinical features of thrombotic thrombocytopenic purpura (TTP) developed during the terminal illness in 14 patients, 7 of whom also had pathological evidence of TTP. Correlation between neuropsychiatric disorders and brain lesions could be made in approximately half the patients. This study indicates that cardiac emboli from Libman-Sacks endocarditis and TTP are common pathogenetic factors of CNS disease in systemic lupus erythematosus, whereas CNS vasculitis is rare.