The clinical and pathologic findings are reported in seven consecutive patients with progressive and fatal pulmonary hypertension which was not explained by predisposing cardiac or pulmonary diseases. Pulmonary arterial lesions consisted of atherosclerosis of the elastic pulmonary arteries, and medial hypertrophy and concentric laminar fibrosis of the muscular pulmonary arteries in seven patients, plexiform lesions in six patients and necrotizing vasculitis in one patient. Pulmonary emboli were not identified. Five patients had manifestations of autoimmune disease, including laboratory abnormalities (positive antinuclear antibody, positive latex agglutination for rheumatoid factor, hypergammaglobulinemia or antimitochondrial antibody) in four, necrotizing vasculitis in one, Raynaud's phenomenon in two and clinical evidence of multisystem collagen vascular disease in two. Five patients had liver disease which developed prior to or concomitant with the onset of pulmonary hypertension. At autopsy, one patient had prominent periportal fibrosis and four had macronodular (postnecrotic) cirrhosis (active in three and inactive in one). Four of these five patients with liver disease and pulmonary hypertension had evidence of autoimmune phenomena. The findings in the seven patients suggest an association between autoimmune disease, plexogenic pulmonary hypertension and liver disease of the chronic active hepatitis-postnecrotic cirrhosis type.