This is a prospective study done on Bangladeshi people during the period from January 1999 to December 2002. Cases were collected from the department of Medicine in Sir Salimullah Medical College, Dhaka; Sher-e-Bangla Medical College, Barisal and Bangabandhu Sheikh Mujib Medical University, Dhaka. We examined the chronic effect of smoking on brain atrophy quantitatively with Computed Tomography (CT). Study was performed on 219 smokers and same numbers of non-smokers from 40 to 70 years old with neither neurological nor focal abnormality in brain CT. Brain atrophy index (BAI) which was a quantitative marker of brain atrophy reported previously, was calculated from each brain CT. Smokers showed a significant increase in BAI compared to non-smokers in groups 50-54 years (p<0.01), 55-59 years (p<0.01), 60-64 years (p<0.05) and 65-70 years (p<0.05). It was suggested that age-related brain atrophy was increased by chronic smoking through advanced atherosclerosis.