First described in 1897, pulmonary arteriovenous malformation (PAVM), although uncommon, should be included in the differential diagnosis of pulmonary nodules, especially when associated with hypoxemia. PAVMs are direct communications between pulmonary arteries and veins, usually with an intervening thin-walled aneurysm. PAVMs may be present at birth, but in most cases they remain unrecognized and asymptomatic until the fourth to sixth decade of life. In approximately 80% of patients with PAVMs, hereditary hemorrhagic telangiectasia is the underlying disease, whereas most of the remainder are idiopathic. Due to the resulting right-to-left shunt, PAVMs may produce dyspnea, cyanosis, clubbing, and pulmonary bruit, although this classical presentation is uncommon. In patients with PAVMs, digital clubbing has been described only in those with large shunt and severe hypoxemia. The most common symptom is dyspnea on exertion, which occurs in approximately 50% of patients with PAVMs. Hemorrhagic complications, either massive hemoptysis or spontaneous hemothorax, occur in approximately 15% of untreated patients, and can be fatal.