Pulmonary arteriovenous fistula (PAVF) is an abnormal connection between pulmonary arteries and veins. Patients with PAVF may have the Rendu-Osler-Weber syndrome, a disease transmitted by autosomal dominant mechanisms. Here we describe a case of PAVF in a 56-year-old woman, who was admitted to our department because of dyspnea, hemoptysis, and a mass in the left lower lung found on chest X-ray. The diagnosis of PAVF was suspected according to clinical and physiological criteria and confirmed by magnetic resonance imaging of the chest. The PAVF was removed by left lower lobectomy. Anamnestic and clinical investigations of the patient's relatives led to the diagnosis of the Rendu-Osler-Weber syndrome.