Eighty-six cases of thoracic outlet compression syndrome have been investigated over the last eight years. In contrast to most series, vascular causes have predominated over neurological causes. Arterial compress can be simple and intermittent; complicated by atheroma, aneurysm, thrombosis or injury. Selected cases of simple compression are dealt with by transaxillary resection of the first rib. Complicated cases require supraclavicular exposure of the subclavian artery. Venous compression seems to be a necessity for the development of acute subclavian thrombosis. The place of thrombectomy with decompression is not yet established in the acute phase. Decompression by removing the first rib is useful in relieving the chronic post-phlebitic symptoms through the rationale is not clear. Chronic intermittent venous obstruction forms a distinct clinical group and the cases always benefit from resection of the first rib. Neurological cases are the most difficult to diagnose with certainty. Only pain in the ulnar nerve distribution can be considered. Signs of diminished sensation and motor weakness affecting the intrinsic muscles of the hand confirm the diagnosis. Nerve conduction tests have been helpful only in a few cases. Where serious conduction impairment is shown recovery after surgery is incomplete.