Acquired arteriovenous fistulas, which are caused by arterial or venous puncture, are common in patients with a history of hospitalization in the intensive care unit for a long time. A four-month-old girl, who was born at 25 weeks and treated in the neonatal intensive care unit for one month due to respiratory distress, was admitted to our clinic with complaints of swelling and bruising on the right arm. Doppler ultrasound revealed an arteriovenous fistula located between the basilic vein and brachial artery, which was surgically treated. Unlike adults, fistulas during infancy may lead to a variety of morbidity, including heart failure, if left untreated. Herein, we report a rare pediatric case of an arteriovenous fistula and discuss our clinical approach.