Authors retrospectively analysed 55 brain CT scans of 47 patients with acute carbon monoxide(CO) poisoning. The Ct scan was taken within 24 hours following CO exposure in all patients, eight of whom had follow-up CT scans taken two to 50 days after initial Ct scan. The results were as follows : 1. Of all 47 cases, low density lesion on CT was demonstrated in 37 cases(79%), brain edema in 6 cases, hemorrhage in 3 cases, basal ganglia calcification in 2 cases and cerebral atrophy in 2 cases. 2. Of 37 cases with low densities, the lesion was located in the cerebral white matter in 27 cases and in basal ganglia in 16 cases. 3. Of 16 cases with basal ganglia lesion, most of them(11 cases) showed the lesion in the globus pallidus bilaterally. 4. Of 8 cases with follow-up CT scan, 5 cases, in whom CT scan was taken after 3 weeks or more, showed improvement of brain edema.