The study focuses on the assessment of chromosomal damage associated with folate and vitamin B12 deficiency, and with cigarette smoking in a tissue directly exposed to cigarette smoke (buccal mucosa) while controlling for potential confounding factors. A cross-sectional study was carried out among 39 current smokers (CSs) and 60 noncurrent smokers (NCSs). Buccal mucosal cells, saliva, and blood samples were collected from each subject. The Health Habits and History Questionnaire (Block et al., 1986) was modified to obtain dietary and other relevant information. Methods used to measure folate, vitamin B12 levels, and the frequency of micronucleated cells in buccal mucosal cells gave reproducible results. The study results suggest that CSs have buccal mucosal folate and vitamin B12 levels that are lower than those among NCSs. CSs were three times more likely to have micronucleated buccal mucosal cells compared to NCSs. There appeared to be no association between low buccal folate and vitamin B12 levels chromosomal damage. The salivary vitamin B12 concentrations and plasma vitamin C and E concentrations, however, seem to be marginally protective against the occurrence of buccal mucosal micronuclei, whereas plasma beta-carotene seems to increase the occurrence of micronuclei. Overall, the results do not support the concept that localized folate and vitamin B12 deficiencies in the buccal mucosal cells of smokers are associated with chromosomal damage in those cells. The presence of vitamin B12 deficiencies in the buccal mucosal cells of smokers are associated with chromosomal damage in those cells. The presence of vitamin B12 in the immediate environment (saliva) and vitamin C and E in the plasma, however, appear to be marginally protective against chromosomal damage in buccal mucosal cells.