In 225 patients requiring reoperation for recurrent thoracic outlet syndrome, "pseudorecurrences" were noted in 43 patients not relieved of symptoms after the initial operation. Such recurrences were associated with technical errors at the initial operation including resection of the second rib instead of the first, resection of the first with a cervical rib left in place, or resection of a cervical rib with an abnormal first rib left. True recurrences occurred in 182 patients, 154 of whom had a substantial piece of rib remaining from the initial procedure. Indications for reoperation included persistent pain, ulnar nerve conduction velocity of 60 m/sec or less (normal, 72 to 82 m/sec), and failure of appropriate physical therapy. Reoperation involved neurolysis of the brachial plexus, decompression of the vessels, and dorsal sympathectomy performed through a posterior thoracoplasty incision. One hundred seventy-seven patients (79%) had improvement, 32 (14%) had moderate improvement, and 16 (7%) were either considered failures or had recurrent scarring.