No difference was observed in genotype distribution and allele frequency between periodontitis patients and control, which means no significant association was identified between IFN-γ +874A/T polymorphism and periodontitis by the comparison of 5 genetic models (T vs A: OR  =  1.01, 95% CI: 0.90–1.13, P  =  .878; TT vs AA: OR  =  1.07, 95% CI: 0.87–1.32, P  =  .537; AT vs AA: OR  =  1.00, 95% CI: 0.81–1.23, P  =  .996; TT+AT vs AA: OR  =  1.00, 95% CI: 0.84–1.19, P  =  .990; TT vs AA+AT: OR  =  1.03, 95% CI: 0.86–1.23, P  =  .733; Figs. 2–6, Table 2). Here, IFNG is linked to periodontitis.