5 (group 1) of 9 patients with systemic lupus erythematosus (SLE) who underwent a kidney biopsy during a 1 -year period had a noninflammatory renal microangiopathy which significantly narrowed or occluded the lumens of arterioles and terminal segments of interlobular arteries. Though these lesions resemble those of malignant hypertension and the thrombotic microangiopathies, their distinctive features, revealed by light, immunofluorescence and electron microscopy, differentiate them from the others. 4 of these 5 (group 1) patients developed hypertension; in 3 the microangiopathy predated the hypertension. None of the remaining 4 (group 2) patients without these lesions has become hypertensive. One group-1 patient with extensive lesions involving 40 % of intrarenal arterioles at biopsy developed renal failure shortly thereafter with increasing arteriolar involvement but unchanged glomerular histology.