The efficacy and safety of azithromycin prophylaxis of community-acquired pneumonia (CAP) in young adults in a military training centre of the Ministry of Defence of the Russian Federation located in the Central European Region of Russia were studied. Two prophylactic regimens with azithromycin vs. the control were evaluated: azithromycin, 500 mg/w for 8 weeks (R1), azithromycin, 1500 mg once upon the enrolment (R2) and no drugs (R3). Nasopharyngeal carriage of Streptococcuspneumoniae and its susceptibility to antibacterials were estimated thrice: before the exposure, after the exposure within the 9th week and after the exposure within the 20th week. The MLS(B) phenotype was suspected when the isolates were resistant to erythromycin and clindamycin. During the observation period of 22 weeks CAP was diagnosed in 20.2% of 678 subjects in group R3, 8.6% of 508 subjects in group R1 (Risk Ratio =0.4, 95% Cl = 0.3-0.6) and 10.3% of 507 subjects in group R2 (Risk Ratio = 0.5, 95% Cl = 0.4-0.7). The S.pneumoniae carriage rate at visit 0 was 34-35%, within the 9th week it was 75, 66 and 50% (p