Aim: Thoracic outlet syndrome (TOS) is a clinical diagnosis treatable by excision of the first rib. This study was undertaken to assess the alleviation of symptoms following trans-axillary rib excision in patients with a diagnosis of TOS suggested by a positive Elevated Arm Stress Test and, by inference, to estimate the prevalence of the syndrome. Method: A retrospective review of trans-axillary first rib excision was performed, No referrals were accepted from outwith the catchment area of our hospital. Post-operative symptomatic improvement was accepted as a confirmation of correct pre-operative diagnosis. Results: Over six years, 52 rib resections were performed in 46 patients, mean age (+/-S.D.) 38.8 (+/-.10.6) years. The indications for surgery were principally neurological symptoms (n=42 excisions), arterial compromise (n=5) and venous compromise (n=5), Symptoms had been present for a mean of 15.8 months prior to surgery. The median follow-up after surgery was 33 months. 42 patients (48 resections) showed immediate improvement in symptoms following surgery, although symptoms recurred in three patients (4 resections) between 6 and 8 months post-operatively, In the final two years of this study, 20 resections resulting in symptomatic improvement were performed, suggesting a prevalence for TOS of at least 10 per 100 000 per year. Conclusions: Thoracic outlet decompression was performed more frequently in this series than many previous reports, suggesting that TOS map be under-diagnosed.