Brain atrophy during normal aging and its relation to chronic smoking was studied using quantitative volumetric measurements of computed tomography. Study was performed about 159 smokers and 194 non-smokers with no neurological abnormality nor focal abnormality in CT scans. Each pixel of head CT scans was computed and Brain Volume Index (BVI) was calculated. BVI showed a significant decrease in smokers compared to non-smokers in three age groups, 50-to-54, 55-to-59 (p<0.001, both) and 65-to-69 (p<0.05). A dose-response study in the male showed that BVI in smokers was significantly lower than that for non smokers. Mean BVI tended to decrease when the smoking index increased but the trend was not significant. The systolic blood pressure and serum triglycerides of smokers were significantly higher than non-smokers (p<0.002 and p<0.05). It was suggested that age-related brain atrophy was enhanced by chronic smoking. Previously we showed that cerebral blood flow (CBF) was significantly lower in smokers than in non-smokers. Then, we suggest the following hypothesis; smoking chronically advances atherosclerosis, both atherosclerosis and high blood pressure reduce CBF, reduced CBF accelerated the lose of neurons which finally renders the brain atrophic.