Aim: The aim of this study was to analyze cytologically the buccal mucosa, tonge dorsum and floor of the mouth in diabetic patients and healthy volunteers to determine what cellular changes are affected by diabetes mellitus. Method: In order to evaluate cellular changes induced by diabetes mellitus, exfoliative cytology was used for the analysis of buccal mucosa, tongue dorsum and floor of the mouth smears obtained 30 type 1 diabetic patients and 40 healty volunteers. Result: Cytoplasmic geometric volume of these cell were 93974.37 in tongue, 82104.23 in floor of the mouth and 114373.33 in buccal mucosa in the type 1 diabetic patients. Cytoplasmic geometric volume were 133043.67 in tongue, 113914.45 in floor of the mouth and 165397.38 in buccal mucosa in the control group. Our nuclei geometric volume values were 454.907 in tongue, 626.771 in flor of the mouth and 652,868 in buccal mucosa in the type 1 diabetic patients. Nuclei geometric volume values were 347.149 in tongue, 445.427 in flor of the mouth and 342.592 in buccal mucosa in the control group. NA (nuclei) was markedly higher (p<0.005) in the diabetic patient group, also, cytoplasmic volume exhibited a statistically significant difference (p=0.000) between these two groups. Cytoplasmic volume was markedly higher (p=0.000) in the control group. Conclusion: The findings suggest that there was an alterations in oral epithelial cells, detectable by microscopy and cytomorphometry in diabetic patients undergoing insülin treatment. Further research is needed to determine related factors. It may play an important role in the early detection of diabetes mellitus.