Previously reported from our institution has been a series of 63 patients with pulmonary arteriovenous fistula who were seen from Jan. 1, 1952, through Dec. 31, 1972. Subsequently, we have seen 38 additional patients during the 8 1/2-year period from Jan. 1, 1973, through June 1981. The series includes three patients with hereditary telangiectasia who had bilateral pulmonary arteriovenous fistulas removed at two separate thoracotomies. Our report also includes a brief description of five additional patients with acquired systemic artery-to-pulmonary artery fistula who underwent miniballoon occlusion of the fistula. We are including these five cases because we believe this therapeutic catheterization technique may be of particular value in patients with multiple or bilateral pulmonary arteriovenous malformations and may obviate extensive pulmonary resection and repeat thoracotomy. Pulmonary arteriovenous fistula is believed to occur most often in middle-aged women who have associated Rendu-Osler-Weber syndrome, but most of our patients did not have hereditary hemorrhagic telangiectasia. Twenty-three (36.5%) of the 63 patients in a previous Mayo Clinic series and 18 (47%) of the 38 in the present series had associated Rendu-Osler-Weber syndrome. A logical workup of a patient with pulmonary arteriovenous fistula includes, in sequential fashion based on priority, chest roentgenography and tomography, arterial blood gas measurements, contrast echocardiography with indocyanine green dye, angiography, and measurement of differential pulmonary venous oxygen content.