We evaluated whether rotavirus vaccination is associated with the incidence of type 1 diabetes among children. We designed a cohort study of 1,474,535 infants in the United States from 2001-2017, using data from a nationwide health insurer. There was a 33% reduction in the risk of type 1 diabetes with completion of the rotavirus vaccine series compared to the unvaccinated (95% CI: 17%, 46%). Completion of the pentavalent vaccine series was associated with 37% lower risk of type 1 diabetes (95% CI: 22%, 50%). Partial vaccination (incompletion of the series) was not associated with the incidence of type 1 diabetes. There was a 31% reduction in hospitalizations in the 60-day period after vaccination (95% CI: 27%, 35%) compared to unvaccinated children. Overall, there was a 3.4% decrease in incidence annually in children ages 0-4 in the United States from 2006-2017 which coincides with the vaccine introduction in 2006. We conclude that rotavirus vaccination is associated with a reduced incidence of type 1 diabetes. Rotavirus vaccination may be the first practical measure that could play a role in the prevention of this disease.