A thrombotic microangiopathy that is identified in patients with the antiphospholipid syndrome (APS) represents only a part of the vascular pathology that can be associated with antiphospholipid antibodies (aPL). Tissues from two autopsies, four renal biopsies, two skin biopsies, and one amputated leg were obtained from six patients who met criteria for the diagnosis of APS. Three patients had systemic lupus erythematosus (SLE), one had lupus-like disease, and two had a primary APS. Five of the patients were hypertensive. Arteries of three patients disclosed fibrin thrombi along with widespread obstruction by recanalized intimal connective tissue. Small renal, leptomeningeal, and pulmonary arteries showed concentric cellular and fibrous intimal hyperplasia indistinguishable from hypertensive vascular disease. Glomerular capillary and afferent arteriolar thrombi were found in renal biopsies from two SLE patients. One of these SLE patients required a leg amputation in which the popliteal artery demonstrated thrombosis, intimal hyperplasia, and acute inflammation. The findings support clinical and experimental data that indicate aPLs cause thrombosis but suggest diversity in the pathogenetic mechanisms aPLs are capable of promoting. Inflammation seems to be rare and to accompany thrombosis. Intimal hyperplasia is particularly common. Its involvement of renal arteries may contribute to hypertension that develops in some APS patients.