Thoracic outlet syndromes (TOS) are a group of disorders in which there is compression of the brachial plexus or the subclavian artery or vein or both as they pass through the thoracic outlet. Most patients have neurologic symptoms of the arm and hand. These syndromes are generally named according to the site of compression or the compressing structures. There are many factors that predispose patients to the development of TOS. The differential diagnosis includes many diseases that can add to or imitate TOS symptoms. Diagnosis is based mainly on the findings of the history and physical examination. Most patients respond well to a conservative care regimen, which should be tailored to the individual patient's needs. In most instances, surgery should be reserved as a treatment of last resort.