Tobacco smoking is a global problem associated with the occurrence of many systemic diseases and tumors. Oral cavity tumors are common tobacco-related cancers, and of all the anatomical structures that are exposed to the effects of smoking, the oral cavity remains the least-explored area. Changes that occur in the biology of oral epithelial keratinocytes under the influence of the components of tobacco smoke often go unnoticed, if they are asymptomatic. The proper functioning of the oral epithelium is determined by the proliferation and differentiation of the cells in keratinization — the process of programmed cell death, which extends through to the mechanisms of apoptosis. Due to incomplete knowledge of the impact of tobacco smoke on the biology of keratinocytes, an evaluation of the cell cycle was conducted and the apoptosis of oral epithelial keratinocytes was analyzed. The study involved 77 patients divided into four groups according to their intensity of smoking, ranging from 0 to 27 pack-years. There were no differences in the cell count between nonsmokers and smokers in the proper cell-cycle phases. The percentage of proliferating cells in the oral epithelium is about 11%. A reduction in the number of early-apoptotic cells (caspase positive/propidium iodide negative) and an increase in the number of late-apoptotic cells (caspase positive/annexin V positive/propidium iodide positive) were observed to occur with increasing pack-years. The present study demonstrates that smoking does not affect the oral keratinocyte cell cycle, but does modify the number of cells with early and late apoptotic features. An intensification of the impact of tobacco smoke components on the biology of the oral keratinocytes is clearly noticeable at approximately 6 pack-years. This indicates that the biology of the first organ exposed to tobacco smoke — the oral epithelium — is altered by tobacco smoking. (Folia Histochemica et Cytobiologica 2014, Vol. 52, No. 1, 60–68)