From January 1980 to August 1983, 213 patients with carbon monoxide poisoning were seen; 131 received hyperbaric oxygen and had no sequelae. Eighty-two patients were treated with normobaric oxygen; ten (12.1%) returned with clinically significant sequelae. The specific neurological sequelae included headaches, irritability, personality changes, confusion, and loss of memory. This recurrent symptomatology developed within one to 21 days (mean, 5.7 days) after the initial exposure, although no reexposure occurred. These recurring symptoms resolved rapidly with hyperbaric oxygen therapy. We recommend that hyperbaric oxygen therapy be used whenever CO poisoning symptoms recur.