PurposeTo estimate and compare annual prevalence and incidence, and demographic characteristics of patients with ulcerative colitis (UC) in Japan and the United States (US).MethodsAll patients with UC were identified from large employment-based healthcare claims databases (Japan Medical Data Center [JMDC] in Japan and IBM MarketScan Commercial Claims and Encounters database [CCAE] in the US), from 2010 to 2019. Cases were confirmed using International Classification of Disease-9/10 codes with/without Anatomical Therapeutic Chemical codes. Annual age-standardized prevalence and incidence rates were estimated for the JMDC by direct standardization using the CCAE as the standard population.ResultsPatients with UC were younger in Japan than in the US and men were affected more than women, whereas the reverse was true in the US. Annual prevalence per 100,000 population increased significantly from 5 in 2010 to 98 in 2019 in Japan and from 158 to 233 in the US. Prevalence increased in men more than in women and in all age groups in Japan, whereas increases were observed similarly in men and women, and in the 6 to < 65-year age groups in the US. Annual incidence per 100,000 person-years increased significantly over time in both sexes and in all age groups in Japan, with higher increases in women and in ≥ 18 year-olds. UC incidence rates did not change over time in the US.ConclusionTen-year trends in epidemiology of UC differ between Japan and the US. The data point to a growing disease burden in both countries that warrants investigation of measures for prevention and treatment.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00384-023-04417-6.