The role of brain computerized tomography (CT) imaging in predicting clinical outcome was investigated in patients receiving hyperbaric oxygen therapy for serious carbon monoxide (CO) poisoning. From a series of 48 consecutive patients suffering loss of consciousness from CO exposures, the records of 40 selected patients were evaluated to determine how their CT findings correlated with clinical outcome. A neuroradiologist blinded to patient outcome confirmed the radiographic findings. CT abnormalities consisted of globus pallidus hypodensities (nine patients), subcortical white matter hypodensities (four), cerebral cortical lesions (one), cerebral edema (one), hippocampal lesions (one), and complete loss of gray-white differentiation (one). Of the patients with globus pallidus lesions, 44% manifested incomplete recovery, whereas white matter lesions reflected a 74% incidence of morbidity. Age, duration of CO exposure, and interval between CO exposure and treatment did not significantly relate to clinical outcome. The blood carboxyhemoglobin levels correlated with clinical prognosis (P < 0.05) and, importantly, CT results significantly predicted clinical outcome (P < 0.05). A normal scan correlated highly with a complete recovery, whereas an abnormal scan predicted incomplete recovery or death, despite prior HBO therapy. The current study establishes prognostic validity for brain CT imaging for evaluating clinical outcome after HBO therapy for CO poisoning.