Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterized by the presence of telangiectases and arteriovenous malformations. In some families in whom a form of idiopathic pulmonary arterial hypertension cosegregated with HHT, mutations in the ACVRL1 gene were present.We noninvasively measured the pulmonary artery systolic pressure (PASP) in a group of patients with HHT.Doppler transthoracic echocardiography and mutation analysis by direct sequencing were used.We studied 68 patients (age 19-84 years, mean 50.75 + 15.11; 32 females) and PASP measurement was possible in 44 (64. 7%); in addition, 9 of them (20.5%) showed elevated values. Molecular analysis identified mutations in the ACVRL1 gene in 7 of these 9 subjects. Even on exclusion of relatives of the single case with known pulmonary hypertension, 5 of 37 patients (13.5%) still showed values higher than those of controls.The data indicate that elevated PASP values are a frequent and previously unrecognized complication of HHT. Because clinically significant pulmonary artery hypertension (a relevant cause of morbidity and mortality) may subsequently develop in these patients, we propose that the measurement of PASP should be included among the parameters recorded for all patients undergoing Doppler transthoracic echocardiography during routine clinical screening.