BackgroundAcute diarrhoea remains one of the leading causes of morbidity and mortality worldwide. Most existing research has focused on children younger than 5 years of age, while data from Thailand are limited. In this study we characterised trend of diarrhoeal admissions, associated Disability-adjusted life years (DALYs) and determined predictors of mortality and high-cost admissions in Thailand.MethodsWe analysed Thailand's National Health Security Office inpatient claims database for 2014-2022. We estimated admission rates (ASRs), costs of admission ($PPP), and DALYs for pre-pandemic (2014-2019) and pandemic (2020-2022) periods. Predictors of mortality and high-cost admission were assessed using logistic regression. Rotavirus vaccine impact was evaluated among children younger than 5 years of age.FindingsAmong 3,041,699 total admissions, 54·3% were female, median age was 22 years (IQR 3-61). ASR fell from 686·5/100,000 pre-pandemic to 474·5/100,000 pandemic, while mean cost rose from $PPP 372 to 539. The case fatality ratio was 0·6 (18,782 deaths). Total burden was 1,124,618 DALYs; mean annual DALYs fell from 132,366 to 110,140. Children younger than 5 years of age accounted for 31·4% of admissions, whereas adults older than or equal to 60 years of age accounted for 25·7% of admissions and 64·6% of total deaths. Older age, male sex, referral hospitals, central region, stroke, sepsis, respiratory failure, and Salmonella or Clostridioides difficile infection was associated with mortality or high-cost admission. Each 1% increase in rotavirus vaccine coverage was associated with 2·0% reduced rotavirus admissions.InterpretationThailand's diarrhoeal admissions were concentrated among young children and older adults, with mortality and high-cost admissions driven by Salmonella and C. difficile infections. Improved water, sanitation, rotavirus vaccination, and hospital preparedness are essential to tackle the diarrhoeal disease burden.FundingThis research was funded by Wellcome (grant number 315982/Z/24/1). For the purposes of open access, the authors have applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission.