THIS study includes a series of cases in which the subclavian artery and brachial plexus were compressed between the clavicle and the first rib. In a previous paper1 a series of 9 cases of cervical rib were reported, in 5 of which costoclavicular compression of the neurovascular structures leading to the arm was the outstanding feature. In the present series of 14 cases a cervical rib was actually present in only 2. In the remaining 12 the compression was between the clavicle and the first thoracic rib. The condition is characterized by vascular and neurologic symptoms together or separately. The pulse to the arm is markedly reduced in volume or shut off entirely when the shoulders are thrown back as in the attention position. On reviewing the literature, one finds many theories formulated in an attempt to explain the mechanism producing symptoms in the socalled scalenus anticus and cervical