Pneumothorax is a rare but significant complication of the supraclavicular brachial plexus block due to the proximity of the brachial plexus to the dome of the pleura. The use of ultrasound guidance has significantly reduced the risk of pneumothorax compared to traditional landmark techniques. In large studies, the incidence with ultrasound is estimated to be approximately 0.04% to 0.06% (or 0.4 per 1,000 blocks), whereas landmark- based techniques have reported rates as high as 6.1%.Diagnosis can be challenging because symptoms are often delayed. While some cases present immediately, many patients do not develop dyspnea or chest pain until 48 to 72 hours after the procedure.Key factors increasing the risk include loss of needle tip visualization during the procedure, operator inexperience, and patient factors such as COPD, smoking, or a high pleural dome. Traditional supine chest X-rays may miss small or ventral pneumothoraces. Upright expiratory X-rays or thoracic ultrasound are preferred for better sensitivity in detecting iatrogenic injury