The relationship of primary pulmonary hypertension to longstanding portal hypertension secondary to hepatic cirrhosis was examined. An unselected series of 17,901 autopsied patients older than 1 yr of age showed that primary pulmonary hypertension occurred with a prevalence of 0.13% in all patients, but with a prevalence of 0.73% among patients with cirrhosis (p less than 0.001). A clinical series of 2,459 patients with biopsy-proved hepatic cirrhosis showed a prevalence of primary pulmonary hypertension of 0.61%, also significant (p less than 0.001) when compared with the prevalence among all patients older than 1 yr of age at autopsy. These data appear to exclude a coincidental association of cirrhosis with the development of the vascular lesions of primary pulmonary hypertension.