Pure word deafness is a rare behavioral disorder in which the comprehension of spoken language is grossly disturbed, but the abilities to speak, read, write, and process nonverbal auditory stimuli remain intact. This disorder is caused by superior temporal gyrus lesions in the dominant hemisphere that isolate Wernicke's area from incoming auditory information. This involved area is supplied by cortical middle and posterior temporal end-artery branches of the middle cerebral artery. Among approximately 100 extracranial-intracranial bypass procedures performed at our institution in the past 5 years, three patients developed the syndrome of pure word deafness. A cortical or posterior temporal branch of the middle cerebral artery was utilized as the recipient artery in each instance. In all cases, the deficit was transient, delayed (i.e. the patient did not awaken from anesthesia with the deficit), and unrelated to the preoperative deficit. The syndrome of pure word deafness may be more common after bypass than is currently recognized. Localized arterial spasm, dysautoregulation secondary to operative manipulation, or focal brain swelling may be operative mechanisms in the development of this and other delayed, reversible deficits related to bypass surgery.