The aim of the work was to establish the relationship between the genotype of the cystic fibrosis transmembrane conductance regulator (CFTR), the level of local immune reactivity and the degree of chronic gingivitis in children with cystic fibrosis. The study has shown significant differences in the local immunity indices of the oral mucosa and the condition of periodontal tissues in children with cystic fibrosis in comparison with the control group. The features of the course of dental pathology among sick children, depending on the type of CFTR gene mutation are determined. Disturbance of mucosal immunity of the oral cavity in children with cystic fibrosis is manifested by a decrease in lysozyme activity in mixed saliva by 1.5 times and level of secretory immunoglobulins IgA by 1.4 times. A consequence of this is an increase of the degree of dysbiosis of the oral cavity by 3.7 times. At the same time, a lesser imbalance in the microflora and lysozyme activity observed in the homozygote group of the F508del mutation, and heterozygotes of the F508del mutation have the most severe manifestations of chronic gingivitis.