The pulmonary vascular changes in systemic lupus erythematosus (SLE) have been investigated from 20 autopsies performed at the Mount Sinai Hospiral from 1964 to 1973. Acute lesions included fibrinoid necrosis and vasculitis. Chronic lesions consisted of intimal fibrosis, medial hypertrophy, alteration of elastic laminae, periadventitial fibrosis, and, in one case, aneruysmal dilatation. These changes were found variously in arterioles, arteries and veins. The fibrotic and occlusive vascular lesions may account for the syndrome of "unexplained breathlessness" that occurs in SLE. These lesions may progress in certain individuals to overt pulmonary hypertension; the concept of coexisting primary pulmonary hypertension and SLE should be re-examined.