Pulmonary involvement in the primary antiphospholipid syndrome (PAPS) has generally been on the basis of thromboembolism. We describe a patient with hemorrhagic alveolitis, a life-threatening complication that must also be considered. The patient was a 63-year-old Caucasian man who had a past history of recurrent deep vein thromboses as well as an arterial occlusion of the left popliteal artery and who developed hemorrhagic alveolitis and capillaritis at age 57 years, which was treated with long-term cyclophosphamide, steroids, and anticoagulation. Four years later, he had a recurrence of the same condition, and a positive lupus anticoagulant test was found. Severe thrombocytopenia, diagnosed as idiopathic thrombocytopenic purpura, was treated with platelet transfusions and increasing steroid dosage. Hemorrhagic adrenal infarction supervened at this time, and a septicemic illness was treated with intravenous antibiotics. Diffuse alveolar pulmonary hemorrhage is an unusual complication of the APS that is being increasingly reported, and recognition of its possible fatal course is of great importance for the treating physician. Severe thrombocytopenia that could contribute to hemorrhage may also accompany the APS, but this is unusual.