Acute gastroenteritis (AGE) often causes different complications in younger children, which can lead to hospital admission. Purpose — to explore the etiological structure of infectious gastroenteritis in children under 5 years and severity clinical features of the disease depending on the pathogen. Materials and methods. 978 children with AGE were enrolled in the study. The age of participants was 0–5 years, they all were patients of infectious diseases department of Kyiv city children's

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... l No.1 during 2014–2018 years. The division into groups was based on the detected pathogen. Determination of rotavirus antigen was performed by enzyme$linked immunosorbent assay (ELISA), other pathogens were identified by nucleic acid extraction and testing by TAC (TaqMan Array Cards). The clinical features severity according to Vesicari's scale were analyzed during the study. Results. Among children who were enrolled in the study the most common pathogen was rotavirus, which was present in 47% of all cases. Norovirus took the second place. Campylobacter was the most common among bacterial pathogens. Rotavirus was more common among children of older age group. Shigella and Campylobacter were two the most common pathogens in younger age group. In group non-rotavirus pathogens the most common were mild and moderate course of the disease, but in group with rotavirus mild course wasn't common. None of children with adenoviral or noroviral infection had mild disease. The most part of AGEs caused by bacterial pathogens had severe course. Conclusions. The leadership of rotavirus infection and an important change in the majority of infections, the introduction of vaccination into the national calendar is highly relevant. Norovirus took the second place in etiological structure of AGE after rotavirus, and that's why developing vaccine against it is an actual problem. According to severity of disease depending on the pathogen, the biggest value for prophylaxis will have development of vaccines against salmonellosis, norovirus and adenovirus. The research was carried out in accordance with the principles of the Helsinki Declaration. The study protocol was approved by the Local Ethics Committee of these Institutes. The informed consent of the patient was obtained for conducting the studies. No conflict of interest was declared by the authors. Key words: causative agents of acute gastroenteritis, rotavirus, noravirus, severity.