Background: Prior case reports have indicated that treating thoracic outlet syndrome (TOS) may relieve intractable migraine headaches, but the reported experience is limited. We report how a strategy to treat concurrent TOS can help relieve migraine headaches in patients with dual diagnoses. Methods: Retrospective chart review for diagnostic and interventional data on patients with migraine and TOS followed by a questionnaire to investigate specific migraine features and changes in headache burden before and after treatment of TOS. Results: 50 patients (48 women, 2 men, age = 43.9+/12.7years) with dual diagnoses of chronic migraine and venous TOS were included (20 migraine with aura, 28 migraine without aura, two hemiplegic migraines). Based on a chart review of available data, headaches had become chronic within one year of onset in 21 patients (42%) and included these characteristics: side-locked or greater headache ipsilateral to limb paresthesia (38/50 patients), presence of limb swelling (32/48 patients), and worsened by recumbency (32/38 patients). Interventions included physical therapy, percutaneous transluminal venoplasty, 1st rib removal, scalenectomy, pectoralis minor tenotomy, and vein patching. Thirty-two patients eventually needed surgery. Mean patient-reported improvement of headaches on the treated side was 72+/-26.7%; 12 patients experienced complete resolution of headaches after surgical treatment of TOS (follow-up 7.2+/-5.2 months). Questionnaire responders reported significant reductions in headache days (18.3+/-8.6 to 11.1+/-10.8 days/month, p<0.0016), severity (7.8+/2.5 to 5.4+/-2.9, p<0.00079), and need for emergency care (3.6+/-4.0 to 0.71+/-1.3 visits/year, p<0.0029) were noted by questionnaire responders after having had their TOS treated. Questionnaire responders and non-responders were not substantially different in underlying clinical features. Conclusions: Chronic migraines can be important manifestations of TOS. Early transition to a chronic state, headaches worsened by recumbency, and headaches with lateralized myofascial pain are clues to a contribution by TOS pathology.