Pulmonary arteriovenous fistulas are anomalous connections between the arteries and veins of a portion of the pulmonary vascular bed. Since the first clinical diagnosis of pulmonary arteriovenous fistula by Smith and Horton in 1939 (13), 200 cases have been reported. The detection by routine chest roentgenograms and photofluorograms of clinically silent spheroid pulmonary lesions has been largely responsible for an increasing frequency of diagnosis. It is now mandatory that a radiologist, confronted with a density in the lung parenchyma, include arteriovenous fistula in the differential diagnosis. This is of prime importance, since the surgical approach may differ from that for the usual “coin lesion.” Case Reports Case I: On Feb. 15, 1958, a 27-year-old Caucasian sailor was admitted to the St. Albans Naval Hospital. A routine chest roentgenogram for discharge from the service revealed a density in the right lower lobe. History and physical examination were unremarkable. A murmur within the right chest co...