Background/purpose: Patients with diabetes mellitus have been associated with gingivitis, periodontitis, salivary dysfunction, altered taste, and candidiasis. Diabetes can cause considerable cellular changes. The aims of this study were to assess the oral manifestations in type 2 diabetic patients and to detect cytomorphometric measurements of oral mucosal cells in type 2 diabetic patients and healthy control subjects by using exfoliated cytology smears. Methods: Samples were collected from 50 adults, aged 30-60 years (25 patients with type 2 diabetes mellitus and 25 non-diabetic healthy persons as the control group). Smears were obtained from two sites, normal buccal mucosa and lateral border of the tongue from each subject. The freshly obtained specimens were assessed for cytomorphometric analysis. An eyepiece micrometer was used to take mean values of ND, CyD, and N: C ratio. Comparison of nuclear diameter (ND), cytoplasmic diameter (CyD) and the ratio of two diameters (N: C) among groups was performed by using ANOVA. Results: The results showed that statistically significant increase in ND (p=0.01 for buccal mucosa and 0.007 for tongue) and N:C ratio (p=0.01 for both tongue and buccal mucosa), with a statistically significant decrease in CyD, was found in diabetic patients compared to controls (p=0.001 for both tongue and buccal mucosa). Conclusion: Diabetes produces definite cytomorphometric changes in the oral mucosal cells of patients. The results suggested that nuclear diameter increased while cytoplasmic diameter was decease in type 2 diabetic patients. The most predominant oral manifestations found in type 2 diabetic patients were periodontal disease and oral dryness.