Introduction:The assessment of micronuclei in exfoliated cells is a promising tool for the study of epithelial carcinogens and can be used to detect chromosome breakage or mitotic interference, thought to be relevant to carcinogenesis.Aim:The present study aimed to detect micronuclei in exfoliated oral mucosal cells in individuals using various tobacco forms from the last 5 years.Materials and Methods:A total of 75 healthy male subjects (25 smokeless tobacco users, 25 smokers, and 25 non–tobacco users) were selected for the study. Smears were obtained with moistened wooden spatula from buccal mucosa and fixed with 95% alcohol. All the cytologic smears were stained by Papanicolaou technique. From each slide, ~1000 cells were examined under the 400× magnification and where micronucleated (MN) cells were located, they were examined under the 1000× magnification.Result:MN cells were found to be significantly higher in smokeless tobacco users than in smokers and controls.Conclusion:A positive correlation is found between increased micronucleus frequency and tobacco-using habits. So micronucleus assay can be used as a biomarker of genotoxicity.