The purpose of the study was to evaluate the effectiveness and prevention of outbreaks of community-acquired pneumonia (CAP) and acute respiratory diseases (ARD). The study included conscripts arrived at a training center. An 8-week course of prevention (curantyl, 100 mg a week) was assessed. The end point of the study was a new case of CAP and ARD. The study covered 2333 persons, of them 2226 completed the study. In the control group (n = 1034), CAP developed in 11.9% of the examinees (95% confidence interval (CI), 10-14%), clinical cases of ARD were observed in 18.7% (95% CI, 16-21%. The same parameters in the prophylaxis group (n = 1192) were 9.6% (95% CI, 8-11%) and 11,7% (95 CI, 10-14%). The relative risk of the diseases for a prevention group was 0.8 (95% CI, 0.7-1.1) (p = 0.34) and 0.6% (95% CI, 0.5-0.8) (p < 0.0001), respectively. The study has demonstrated that dipyridamole is effective and safe as a drug for preventing ARD. The findings were slightly more scarce than those obtained by other authors, which may explain the performance of the study in summer when the role of respiratory viruses and related disease is not so significant.