Twenty-three patients with delayed carbon monoxide (CO) encephalopathy completed a short-term follow-up brain computed tomographic (CT) study. Of them, 12 revealed low-density lesions in the cerebral white matter, 3 had pallidal low-density lesions, and one showed low-density lesions in the cerebral white matter and globus pallidus on initial CT scans. Of the 23 patients with follow-up brain CT scans, 9 (39.1%) showed more aggravating patterns with cortical atrophy . 8 with concomitant low-density lesions in the cerebral white matter. Age, sex, duration of unconsciousness during the anoxic episode and lucid interval did not appear to affect the presence of cortical atrophy, but the cerebral white matter low-density lesions on the initial CT scan seemed to be correlated with cortical atrophy after delayed CO encephalopathy. In conclusion, cortical atrophy after delayed CO sequelae is relatively common, and frequently associate with the cerebral white matter low-density lesions. Follow-up brain CT study will be needed to determine the development of cortical atrophy in all patients with delayed encephalopathy after CO poisoning.