Background and Objectives: Brachial plexus block is used for upper limbs anesthesia. The use of ultrasound-guided (USG) technique for blockade has become popular in recent years, facilitating its execution by providing real-time images of the plexus and surrounding structures while minimizing complications. The purpose of this report is to describe a case of pneumothorax following ultrasound-guided interscalene block., Case Report: Male patient, 49 years old, weight 62kg and height 1.72m, slender, smoker, asymptomatic, ASA II E. The patient underwent surgical repair of right ulna open fracture through USG-guided interscalene brachial plexus block with axillary supplementation. After sedation and antisepsis, the linear probe of the USG apparatus was placed perpendicular to the interscalene groove (12 Hz), and stimucath A50 introduced in plane. After visualization of nerve trunks, 20mL of ropivacaine 0.5% was administered with axillary block supplementation (same volume and concentration of anesthetic). At the end of surgery, the patient complained of respiratory-dependent chest pain associated with dyspnea and decreased pulse oximetry (91% in room air), but hemodynamic stable (BP=130/70 and HR=84 bpm). Although pulmonary auscultation was normal, chest X-ray showed the presence of right pneumothorax. Water seal chest drainage was performed, after which the patient reported improvement of symptoms and was discharged from hospital in good general condition after 8 days., Conclusion: Despite the dynamic visualization of cervical structures with USG, interscalene block may result in pneumothorax. An unusual higher pleural dome due to the hyperinflated lung (smoking) probably facilitated the accidental pleural puncture., (Copyright © 2012 Elsevier Editora Ltda. All rights reserved.)