Effort thrombosis of the subclavian vein (Paget-Schroetter syndrome) has long been considered a primary thrombotic process, but recent experience suggests that it may commonly result from repeated mechanical compression. Increased awareness of the pathophysiology of this syndrome can allow timely, improved diagnostic screening and the use of specific surgical intervention to relieve the venous consequences. During the past 15 years we have treated six patients with mechanical compression in the thoracic outlet causing surgically correctable venous occlusive problems. There were four men and two women with an average age of 38 years (range 26 to 53 years). All patients exhibited pain, swelling, and cyanosis of the upper extremity, with worsening venous congestion on abduction of the arm. Five of six patients were originally treated for effort thrombosis of the subclavian vein with arm elevation and anticoagulation; two also underwent immediate thrombolytic therapy with urokinase. Venography was prompted in each case by positional symptoms during follow-up and showed irregular stenosis of the subclavian vein adjacent to the first rib. All patients underwent extended first rib resection and circumferential venolysis (one patient underwent bilateral procedures); one was performed through a transaxillary approach, two through a supraclavicular approach, and four through a new, "paraclavicular" approach. All subclavian veins appeared normal after venolysis. Five of six patients also underwent complete scalenectomy and brachial plexus neurolysis. In each patient, venous and neurogenic symptoms resolved and venography confirmed a patent subclavian vein, with follow-up ranging from 11 months to 13 years (mean 3.8 years).