The occurrence of non-tuberculous non-tumorous respiratory diseases in children and in adults was investigated in a population of approximately 28 300 inhabitants from selected health communities of a Prague industrial district between October 1, 1976 and December 31, 1978. In the course of this period such a disease occurred once at least in 31% of the population. Of a total of 17 133 respiratory disease cases, acute upper respiratory infections occurred in 72.0%, acute bronchitis in 12.2%, influenza in 12.5%, pneumonia in 1.3%, chronic bronchitis in 0.3%, bronchial asthma in 0.6% and other respiratory diseases in 0.5%. Repeated respiratory diseases with four or more episodes of a disease in the course of one year occurred in 6.0% of preschool-age children (0-5 years of age), in 2.8% of school-age children (6-14 years of age), and in 0.2% subjects from the age of 15. Differences in the morbidity rate among the three age groups were statistically significant. In most cases repeated respiratory diseases began to occur after the entry of children to collective institutions. The most frequent respiratory diseases as a cause of incapacity for work were acute upper respiratory infections and influenza with a predominance of incidence in persons younger than 40 years of age. By contrast, in chronic bronchitis as a cause of incapacity for work there was a significant predominance of affected subjects from 40 years of age. The mean duration of incapacity for work due to chronic bronchitis was longer than that due to acute respiratory diseases. In respiratory diseases chronic bronchitis was found to be the most frequent primary cause of death, while pneumonia was quite often an immediate cause of death in the subjects weakened by other diseases.