['The most important risk factor linked to the development of oral leukoplakia (OL) and oral squamous cell carcinoma (OSCC) is tobacco use. Tobacco contains carcinogens that influence the DNA repair, cell cycle control and may produce chromosomal aberrations. The loss or acquisition of one or more chromosomes is defined as aneuploidy.', "Aneuploidy was determined by means of the DNA-content included in cells obtained by exfoliative cytology and Feulgen's staining. The cells were collected from the clinically healthy lateral margin of the tongue of non-smokers without oral lesions, smokers without oral lesions, smokers with OL, and smokers with OSCC, using the CytoBrush(®). Each group was composed of 20 individuals. A Carl Zeiss image analyzer system and the KS300 software were used. Statistical analysis was performed with BioEstat(®) software.", 'The mean percentage of aneuploid nuclei was statistically higher in the smokers (79.65%), smokers with OL (68.4%), and smokers with OSCC (93.65%), as compared to non-smokers (39.3%) (P<0.05). A trend toward an increase in the aneuploidy of the smokers with OSCC group (P=0.02), as compared to the non-smoker group, could be observed. No significant difference could be observed as regards the mean percentage of aneuploid nuclei in relation to duration of tobacco use or the number of the cigarettes smoked.'] Do tobacco use increase the number of aneuploid nuclei in the clinically healthy oral epithelium?