Abstract: The article presents the results of determination of the risk of bronchopulmonary tissue lesion in the form of acute bronchitis and community-acquired pneumonia among children with acute respiratory infection depending on the fact of being infected with ‘atypical’ agents or not, by using Bayes’ formulae. Materials and Methods: Total 472 children aged 15 days to 12 years hospitalized with radiologically and clinically confirmed a diagnosis like community-acquired pneumonia, acute bronchitis, bronchial asthma, acute respiratory infection, were examined. The control group consisted of 127 healthy children aged 3 to 12 years. Material for the study included sputum, swabs from the posterior pharynx vault, blood, saliva in case of children under 12 months. Results: The results of the study showed that the bronchopulmonary tissue lesion in the form of bronchitis or pneumonia occurred in case of M. pneumoniae (26.8%); M. hominis (18.3%). The frequency of C. pneumoniae in inflammatory respiratory diseases was low. The probability of bronchopulmonary tissue lesion in case of Cytomegalovirus was 48.6%. This fact was associated with a high prevalence of the pathogen in inflammatory respiratory diseases and might indicate the aggravating role of Cytomegalovirus in the development of such diseases. It could be assumed that Cytomegalovirus in combination with other pathogens would lead to bronchopulmonary tissue lesion in the form of bronchitis or pneumonia. The same value as for Cytomegalovirus was obtained for Epstein-Barr virus (45.4%). The role of Herpes simplex in the development of pneumonia and bronchitis was low, or 7.7%, relative to 92.3% that the disease would develop like an acute respiratory disease with the same pathogen.