Although the transaxillary route appears to be the optimal approach in patients with thoracic outlet syndrome (TOS), the effect of clinical features on surgical outcome remains unclear. We conducted a study to determine the clinical predictors of surgical outcome in patients with TOS. We examined the data charts of patients with TOS who underwent operation via transaxillary approach. We investigated the possible correlations between the clinical features and surgical outcomes, and analyzed the data with logistic regression model to clarify the effect of clinical features on surgical outcome. A total of 127 patients with a mean age of 32.1+/-10.0 years (range 14-62 years) were analyzed. The rates of favorable and poor surgical outcomes were 82.7 and 17.3%, respectively. The subgroups of symptom duration (P=0.023), the subgroups of ulnar nerve conduction velocity (P=0.033) and the presence of cervical rib (P=0.003) showed a significant correlation with surgical outcome. Multivariate analysis revealed that the shorter duration of symptoms (P=0.017) and the presence of a cervical rib (P=0.026) had a significantly unfavorable effect on surgical outcome. The shorter duration of symptoms and the presence of a cervical rib may imply an unfavorable surgical outcome in patients with TOS.