In this report, we describe a patient who developed acute renal failure and fatal pulmonary hemorrhage. Autopsy examination revealed pauci-immune necrotizing glomerulonephritis and pauci-immune hemorrhagic alveolar capillaritis. No evidence of granulomatous inflammation or vasculitis other than capillaritis was found in either lungs or kidneys. In addition, histopathologic examination of the upper respiratory tract, liver, spleen, digestive tract, and skeletal muscle was completely normal. The patient's serum sample disclosed antiproteinase 3 antibodies with an immunofluorescence titer of 1:1,600. Although there have been reports of patients with pulmonary-renal syndrome in association with antiproteinase 3 antibodies in the absence of a well-known vasculitic disease, we have not so far seen a case documented by a detailed autopsy study such as is presented here. In view of our findings and those of some other reports on this clinicopathologic condition, we suggest that this might represent a distinct form of vasculitis with exclusive capillary involvement.