Baseball pitchers appear to be prone to aneurysms of the axillary artery and its branches. The cause is probably related to repetitive compression of or tension on the vessels at the level of the pectoralis minor muscle and the humeral head, which is exacerbated by the pitching motion. The incidence of aneurysms of the axillary artery and its branches among pitchers and other athletes is not known, nor is it clear whether pitchers who are at high risk of vascular injury can be identified before irreversible damage to the vessels has occurred. Perhaps patients who have documented compression or occlusion of the vessel with the arm in the abducted, externally rotated position are at higher risk. Screening pitchers to identify those with axillary artery compression, aneurysm, or thrombosis has also not been shown to be effective. Certainly, many pitchers will have some level of compression of the axillary artery with their arm in the pitching position but will never develop any clinical abnormality requiring treatment. Screening would therefore probably lead to a high false-positive rate. It is clear, however, that pitchers who complain of ischemia-type symptoms such as early fatigue or who have evidence of emboli require a complete evaluation to rule out any abnormality of the axillary artery or one of its branches. Orthopaedic surgeons who see pitchers and other athletes involved in repetitive overhead motions need to be aware of this disorder so that they order the appropriate tests and obtain a vascular consultation--and make a prompt diagnosis. Treatment will vary depending on the type of lesion and on which vessel or vessels are involved, and should be decided on by the team of surgeons treating the patient.