Antiphospholipid antibody syndrome (APS) has been shown to be associated with arterial and venous thromboses, recurrent miscarriages, and thrombocytopenia. We describe 3 cases of adult respiratory distress syndrome (ARDS) in patients with primary APS. The autopsy in one patient revealed no evidence of vasculitis, but extensive small vessel thrombosis of multiple organs including the lungs was seen. No infectious process, connective tissue diseases, or pulmonary edema could be documented and there was no clinical or laboratory evidence of vasculitis in the other 2 patients. The 2 patients who survived responded dramatically to intravenous steroids.