Perioperative hearing loss is usually transient and often goes unrecognized. The incidence of low-frequency hearing loss following dural puncture may be as high as 50%. It seems to be due to cerebrospinal fluid leak, and, if persistent, can be relieved with an epidural blood patch. Hearing loss following general anesthesia can be due to a variety of causes and is much less predictable. Mechanisms include middle ear barotrauma, vascular injury, and ototoxicity of drugs (aminoglycosides, loop diuretics, nonsteroidal antiinflammatory drugs, and antineoplastic agents). Hearing loss following cardiopulmonary bypass is usually unilateral and is thought to be due to embo-lism and ischemic injury to the organ of Corti.