China has a low incidence of type 1 diabetes mellitus (T1DM); however, based on the large population, the absolute numbers are high. Our aim was to assess the incidence of childhood T1DM in Beijing during 2011-2020, predicted incidence for 2025-2035, and to determine the incidence of diabetic ketosis or diabetic ketoacidosis (DK/DKA) in this population.Data on patients aged less than 15 years of age with newly diagnosed T1DM between January 1, 2011 and December 31, 2020 was obtained from five tertiary hospitals in Beijing and retrospectively analyzed.In all, 636 children aged less than 15 years were diagnosed with T1DM during 2011-2020. The incidence of T1DM was 3.11-5.46 per 100,000 per year, with an average increase of 5.10% per year. The age-specific incidence for ages 0-4 years, 5-9 years, and 10-14 years was 2.97, 4.69, and 4.68 per 100,000 per year, respectively. The highest average annual increase (7.07%) in incidence was for the youngest age group. DK or DKA was present at the time of diagnosis of T1DM in 84.6% of patients. The age-specific incidence of T1DM among children aged less than 15 years was predicted to be 7.32, 11.4, and 11.52 per 100,000 in 2035 for ages 0-4 years, 5-9 years, and 10-14 years, respectively.The was a gentle increase in the incidence of childhood T1DM during 2011-2020 in Beijing. This increase is expected to continue for the next 15 years.© 2023. The Author(s).