The article is devoted to a pressing pediatric problem – the development of bronchiolitis in childhood. The study presents a series of clinical observations describing the clinical heterogeneity of bronchiolitis in terms of age, taking into account the variability of clinical symptoms, etiological factors and therapy. During the observation, clinical and laboratory differences in the course of acute bronchiolitis in children depending on age were determined. In the younger age group, the clinical picture was characterized by a pronounced intoxication syndrome, a moderate or severe course of the disease, a long hospital stay (14.3±4.2 days), and the inclusion of systemic glucocorticosteroids in the treatment complex. Among the etiologically significant factors, the RS virus and rhinovirus dominated.
In the older age group, disease was characterized by the absent of intoxication syndrome, with mild respiratory failure, and the duration of hospitalization was 7.2±2.4 days. According to computed tomography data, typical manifestations of acute bronchiolitis were observed in the form of areas of “ground glass”, areas of mosaic oligemia with centrilobular nodules (sign of “tree in bud”), and when assessing the respiratory function, an obstructive-restrictive type of disorders was determined.
The course of bronchiolitis obliterans in the examined patient was favorable with rare exacerbations of the bronchopulmonary process, no progression of respiratory failure, and maintenance of normal growth rates and physical development.
Interstitial lymphocytic lung disease in the form of follicular bronchiolitis was diagnosed in one child with primary immunodeficiency - ataxia-telangiectasia (Louis-Bar syndrome).

Keywords: bronchiolitis, children, diagnosis, therapy, etiology