A 40-year-old homosexual man with the acquired immunodeficiency syndrome (AIDS) presented with dyspnea and renal insufficiency. A chest radiograph showed cardiomegaly and prominent pulmonary arteries, without alveolar infiltrates. Swan-Ganz catheterization revealed pulmonary hypertension and no evidence of left-to-right shunt. Liver function tests were normal. He was treated empirically for Pneumocystis carinii pneumonia, but he died 3 days after admission. At autopsy, membranoproliferative glomerulonephritis type III, P. carinii pneumonia, and plexogenic pulmonary arteriopathy were found. The kidney and lung were studied by electron microscopy and immunohistochemistry. Electron-dense immunoglobulin deposits were identified in glomerular capillaries and were confirmed by immunohistochemistry, but the pulmonary plexogenic lesions were negative. The combination of membranoproliferative glomerulonephritis and plexogenic pulmonary arteriopathy has not been described in AIDS to date.