BACKGROUND Angioplasty and stenting of various lesions of the carotid artery is gaining in popularity. Our knowledge of the efficacy and limitations of this promising technology is incomplete. Although Horner's syndrome and its variants have been described after traumatic, spontaneous, or surgical carotid dissection, it has not been reported after carotid artery stenting. METHODS A 36-year-old woman presented with left neck and ear pain and a 3-year history of rushing noises in her left ear. Angiography demonstrated evidence of dissection of the left internal carotid artery at the skull base with a pseudoaneurysm. The pseudoaneurysm was treated with a 6-mm diameter self-expanding stent in a 4-mm diameter left internal carotid artery. A few hours later, she developed partial Horner's syndrome with a subtle ipsilateral ptosis and miosis without anhidrosis. Angiography performed on the next day did not demonstrate further dissection or aneurysm growth but did show distention of the artery wall because of the stent. She did not develop any further sequelae. CONCLUSIONS This case suggests that stretching of the artery wall may result in stretching of surrounding structures. The sympathetic fibers surrounding the internal carotid artery are clearly sensitive to this degree of stretch. Possible complications associated with stretch injury must be considered when choosing the stent diameter.