A 16-year-old girl presented with digital clubbing and peripheral cyanosis. She was first seen at 12 years of age for evaluation of shortness of breath with exertion. Circumoral and peripheral cyanosis had appeared during the previous several years. No family history of cardiac or vascular lesions or other medical problems was elicited. The patient's medical history was unremarkable.Her physical examination was normal with the exception of the circumoral and digital cyanosis with clubbing. Cardiac and chest examinations were normal without murmur or bruit. The ECG was normal. Laboratory tests showed an RBC count of 5.5 million/cu mm; hemoglobin level, 17 g/dL; and hematocrit reading, 50%. Arterial blood gas values on room air were as follows: oxygen saturation, 83%; Po2, 41 mm Hg; and Pco2, 34 mm Hg. The patient had a chest roentgenogram (Fig 1), showing multiple pulmonary nodules. Dye dilution and catheterization were done.