This study was undertaken with the purpose of improving the effectiveness of the preventive treatment of chronic adenoiditis in the children. The open randomized comparative study included 219 children aged from 6 to 7 years presenting with clinical and anamnestic signs of chronic adenoiditis. The study group was comprised of 113 patients given the Streptococcus salivarius K12-based probiotic complex during 30 days in combination with the nasal-douche. The control group consisted of 106 patients treated with the nasal douche alone. The analysis of the results of the study has demonstrated that episodes of exacerbation of adenoiditis on day 30 after the onset of the treatment occurred in 56 (49.6%) children of the study group compared with 95 (88.7%) patients of the control group. Three months later, acute sinusitis was diagnosed in 4 (3.5%) children of the study group compared with 14 (13.2%) ones in the control group. Acute otitis media was documented in 2 (1.8%) and 5 (4.7%) children of the study and control groups respectively. It is concluded that the treatment with the use of the Streptococcus salivarius K12-based probiotic complex permits to decrease the frequency of exacerbations of chronic adenoiditis and its complications in the children and reduces the requirement for medication therapy.