This uncommon syndrome is caused by compression of the posterior humeral circumflex artery and axillary nerve or one of its major branches in the quadrilateral space. Forward flexion and/or abduction and external rotation of the humerus aggravate the symptoms. Discrete point tenderness is always found posteriorly in the quadrilateral space. Patients with appropriate history and physical findings should have a subclavian arteriogram done by the Seldinger technique. A positive arteriogram reveals occlusion of the posterior humeral circumflex artery with the arm in abduction and external rotation. Patients with sufficient symptoms not responding to conservative treatment and having a positive subclavian arteriogram and local tenderness over the quadrilateral space should be considered for surgical decompression. A posterior approach is recommended. Of the 18 patients operated on, eight have had dramatic and complete relief, eight have been improved, and two have shown no improvement.