Introduction: While the overall complication rate is low, a number of complications have been ascribed to shoulder arthroscopy, most commonly stiffness or failure of repair. 2 3 , 2 4 Pseudoaneurysm is a rarely reported complication of shoulder surgery, and this is the first report of a pseudoaneurysm of the acromial branch of the thoracoacromial artery as a complication of shoulder arthroscopy. Prior case reports have documented axillary artery pseudoaneurysm as a complication of open Bankart repair or as the result of injury sustained during regional anesthetic placement. 1 , 4 , 5 , 7 , 9 - 1 1 In contrast, this report of a symptomatic 2.1cm pseudoaneurysm that required vascular intervention appears to be secondary to injury sustained during a common procedure felt to be safely distant from any significant neurovascular structures. However, the acromial branch of the thoracoacromial artery is in close proximity during standard anterior portal placement through the rotator interval and during acromioplasty or coracoplasty procedures, as the vessel runs on the coracoacromial ligament. Orthopaedic surgeons should be aware of this anatomy and consider this complication in patients presenting with a mass after shoulder arthroscopy.