BACKGROUND: Although they are declining, diarrheal diseases remain a significant cause of mortality. Rotavirus is reported to be the most important cause of severe diarrhea in children under the age of five in the prerotavirus vaccine era. This study aimed to determine the rotavirus positivity in diarrheal children in our region and examine the age distribution and seasonality of rotavirus to contribute to epidemiological studies. METHODS: A total of 18,847 stool samples were collected from pediatric patients (0 - 18 years) who presented with diarrhea at the Department of Medical Microbiology, Istanbul University, Istanbul Faculty of Medicine, between March 2011 and December 2021. These samples were examined for rotavirus antigen positivity using a commercial immunochromatographic kit. RESULTS: Rotavirus antigen was detected in 2,353 (12.5%) of the samples. The positivity rates for 2011 - 2021 were 14.9%, 16.1%, 13%, 9.9%, 12.3%, 10.3%, 9.1%, 7.9%, 22.1%, 10.6%, and 12.6%, respectively. Rotavirus seasonality analysis revealed that the season starts in November and ends in May, with the highest rates in March (20.5%) and February (19.9%). The highest positivity rate (41.8%) was found in the 1 - 2 years age group. CONCLUSIONS: Rotavirus remains a leading cause of gastroenteritis in children in Turkey. Monitoring rotavirus epidemiology is crucial, especially for countries without rotavirus vaccines in their national immunization programs.