Aims Gastroenteritis is a digestive disorder among children with symptoms of abdominal cramps, diarrhoea, and vomiting. This study aimed to determine the prevalence of gastroenteritis in children in the Bannu district in 2019, and also contributed for adopting preventive measures to reduce mortality in children. Subject and methods A retrospective study was conducted to determine the prevalence of gastroenteritis in children in Bannu. The data were collected from official registers of admission maintained in the children wards in the Women and Children Hospital, Bannu. Patients with symptoms of gastroenteritis at the outpatient department were admitted to one of the children wards.Results Overall, 1456 children-897 (61.4%) males and 559 (38.6%) females-suffered from gastroenteritis during the study period. The age group ≤6 months demonstrated the highest share (37.8%), followed by >6 m ≤ 1y (35.5%), >1y ≤ 2y (15.8%), >2y ≤ 5y (7.3%), >5 ≤ 10y (3.2%), and > 10y ≤ 15y (0.4%). Overall, 89.1% of cases were from children ≤2 years old and 96.4% of cases were attributed to children ≤ 5 years of age. April demonstrated the highest percentage of prevalence of 17.7, followed by May (13.5%), November (13%), June (11.7%), September (10.4%), October (9.8%), July (9.5%), August (8.4%), March (3.4%), and February (2.6%). The age group ≤6 m was the dominant group during February through May and was replaced by the age group >6 m ≤ 1y during August through November. Conclusion Gastroenteritis showed a reduced prevalence when shifted from lower to higher age groups. Being male and age group ≤6 m showed the highest prevalence of gastroenteritis with the peak of disease in April. Further research is needed to determine the cause-based prevalence of different gastroenteritis cases in the study area.