UNLABELLED: ABSTRACT Objective: Many different forms of smokeless tobacco are used in the world. An interesting kind of smokeless tobacco (Maras powder) is used commonly in lieu of cigarettes in Kahramanmaras and its environs, in Turkey. The object of the present study was to investigate the effects of the Maras powder (MP) on oral mucosa and to examine the expression of Ki-67 in oral mucosa samples taken from MP users. STUDY DESIGN: Expression patterns for markers of cell proliferation (Ki-67) in oral mucosa of 84 MP users and 30 controls were analyzed by immunohistochemistry. RESULTS: Histologically, acanthosis, hyperorthokeratosis, and parakeratosis were found in all 84 formalin-fixed, paraffin-embedded oral mucosal samples of MP users. The spinous cell layer showed large pale staining epithelial cells with pyknotic nuclei. The subepithelial infiltrate was mild. The epithelium was hyperplastic in 17 cases and dysplastic in 67 cases. The dysplasia was mild in 25 cases, moderate in 35 cases, and severe in seven cases. Immunohistochemical findings revealed that with progression of lesions toward malignancy, there was a significant predilection for a basal-suprabasal staining pattern for Ki-67 antigen as compared with the strictly basal staining pattern seen in normal oral epithelium. Expression of Ki-67 antigen was significantly higher in MP users than in the controls (P < 0.001). CONCLUSIONS: Our study has shown that MP may induce epithelial cell proliferation, and that there was a significant positive association of Ki-67 expression and grade of dysplasia in MP users. MP, in contrast to other smokeless tobacco variants, seems to cause mucosal changes, which may transform into oral cancer.