Background: Carpal tunnel syndrome (CTS) is the most frequent peripheral compression neuropathy of the median nerve in the wrist. High-definition ultrasonography can detect and follow up any postoperative complications causing persistent complaint or poor result like hematoma, scarring, nerve damage or incomplete cutting of retinaculum. The aim of the study was to evaluate effect of surgical decompression on cross sectional area (CSA) of median nerve in patients with carpal tunnel syndrome and examine the role of ultrasound as a follow up tool. Methods: The prospective observational study was done on 20 patients with CTS referred for peripheral neurosurgery. All patients were subjected to full history taking, complete general medical examination, electromyelography (EMG), high-definition ultrasonography including cross-sectional area before and after surgical decompression (open fashion or endoscopically). Results: Using EMG, there is statistically significant decrease in distal motor latency (DML) while there is significant improvement in amplitude following surgical decompression (p<0.001).  On using US, there is statistically significant increase in anteroposterior diameter (APD) wrist and decrease in CSA at wrist. There is significant negative correlation between preoperative DML and APD at wrist. There is significantly negative correlated with postoperative DML and pre and postoperative APD at wrist. On the other hand, there is significantly positive correlation with postoperative DML and pre CSA. Conclusions: There is a decrease in size of the median nerve after surgical decompression denoting that the preoperative increase in median nerve CSA at the carpal tunnel is partially reversible. Ultrasonographic parameters correlated with EMG ones so it can be used as an alternative tool for postoperative follow up.