Background: Primary hyperhidrosis is a condition characterized by excessive sweating beyond the physiological needs. Dissatisfaction among patients after sympathectomy for primary hyperhidrosis is primarily due to compensatory hyperhidrosis. This work aimed to evaluate the efficacy of CT-guided Sympathetic nerve block in predicting compensatory hyperhidrosis before performing sympathectomy. Methods: We performed this randomized clinical trial on 36 patients who complained of signs and symptoms of primary hyperhidrosis and were indicated for sympathectomy. All 36 patients underwent CT-guided temporary local sympathetic block at the level of T2 and T3; analysis of cases was done for those who were managed with permanent thoracoscopic sympathectomy regarding the occurrence and grade of compensatory hyperhidrosis after block and after surgery. Results: For patients with absent compensatory hyperhidrosis in Ct guided Sympatheticnerveblock, 42.86% developed compensatory hyperhidrosis after surgery; the sensitivity and specificity were recorded at 33.33% and 40%, respectively. In the mild grade of compensatory hyperhidrosis was present, 21.43% of cases continued to experience mild compensatory hyperhidrosis after surgery. The sensitivity and specificity for this grade were 25% and 80%; for a moderate grade of compensatory hyperhidrosis, 21.43% progressed to experience moderate compensatory hyperhidrosis after surgery, for a severe grade of compensatory hyperhidrosis cases showed a statistically significant increase to 14.29% after surgery, with a significant p-value of 0.0385*. The specificity for this grade was notably high at 85.71%, and the NPV was 100%, resulting in an accuracy of 85.71%. Conclusions: The significant association between the severity of compensatory hyperhidrosis after the block and the development of severe cases after surgery highlights the potential utility of this preoperative assessment