A clinicopathologic autopsy study of the vascular changes in the kidneys of 100 patients with systemic lupus erythematosus was undertaken. Necrotizing arteritis was found in seven patients, mucinous intimal thickening in nine, onion-skin intimal thickening in two, and renal vein thrombosis in two. Active necrotizing arteritis was present most frequently in the arterioles and interlobular arteries, with healing necrotizing arteritis predominating in the arcuate and interlobar arteries. These events were closely related to the activity of glomerular lesions, and immunologic vascular injury seemed to be the causative factor. Rapidly progressive renal failure and severe hypertension had characterized the clinical courses of the patients. Mucinous intimal thickening, present in the arterioles and interlobular arteries, had been accompanied by accelerated hypertension. Although dialysis or accelerated hypertension may have been causes, other factors, including glucocorticoid therapy, must be considered. In one patient with class II lupus nephritis, renal vein thrombosis was considered the cause of the nephrotic syndrome. These vasculopathies, often detected in patients with lupus at autopsy, seem to alter the clinical course.