OBJECTIVE: To evaluate the efficacy of scalene injection in patients with thoracic outlet syndrome. METHODS: We selected 142 patients diagnosed with thoracic outlet syndrome between January 2005 and October 2009. We performed a series of scalene injection with conservative treatment in all cases. Patients rated their pain degrees using a visual analogue scale. We also evaluated the time to return to everyday life and work, and patients' functional capacity. RESULTS: There were no complications or instances of inadvertent somatic or sympathetic ganglionic blockade after scalene injection. Overall, 111 patients (76.5%) experienced improved symptoms after the first set of scalene injection and 128 patients (88.2%) improved after scalene injection followed by conservative treatment. Of the 68 patients who returned to work during the study period, 54 returned within 1 week, and 62 within 2 weeks. Of those who returned to work, 61 reported nearly full functional capacity. We found that scalene injection was more effective in cases of thoracic outlet syndrome related to trauma than in those related to work-related repetitive stress. CONCLUSION: In patients with thoracic outlet syndrome, scalene injection effectively reduces pain. We recommend scalene injection as an adjunct to conservative treatment.