Background. The role of mast cells in periodontal tissue degradation has been established. These cells can be efficient in the etiology of periodontitis by participating in gingival homeostasis and releasing cytokines and enzymes, resulting in connective tissue matrix breakdown. Therefore, the aim of this study was to compare the mast cell counts between patients with moderate and severe periodontitis. Methods. This case‒control study was performed on 15 subjects with severe periodontitis and 15 subjects with moderate periodontitis, who needed periodontal surgical treatment. Incisional biopsies were provided during periodontal surgery. Afterward, the mean counts of mast cells were determined after toluidine blue staining of the samples. Finally, data were analyzed with SPSS. Results. The results of this study showed that mast cell counts in severe periodontitis cases were lower than those in moderate periodontitis. However, there were no statistically significant differences between the two groups (P=0.611). In addition, the mean mast cell counts in males and females did not show a statistically significant difference (P=0.231), although the count was higher in female subjects. Conclusion. Based on the results, no statistically significant differences were found in mast cell counts between subjects with severe periodontitis and those with moderate periodontitis.