Objective: To evaluate the association between uterine leiomyoma (UL) and development of type 2 diabetes mellitus in young women using a nationwide database. Design: Nationwide population-based cohort study Setting: South Korea. Population or Sample: Women aged between 20 and 40 years at baseline who underwent at least one health checkup between 2009 and 2012 and followed until December 31, 2018 Methods: We excluded those who were previously diagnosed with type 2 diabetes mellitus (n = 28,136), those diagnosed with type 2 diabetes mellitus within the first year of entry (n = 1,607), those who had hysterectomy during the study period (n = 18,485), and those with missing data (n = 166,012). Cox proportional hazards models were used to analyze the risk of developing type 2 diabetes according to the presence of UL. Main outcome Measures: Incidence of the development of type 2 diabetes mellitus according to the presence of UL Results: 2,755,790 women were selected and he mean age of the enrolled population was 29.70 y, and mean body mass index was 21.31 kg/m 2. Among 2,541,550 participants, 18,375 (0.72%) women had UL. Over a median 7.45 years of follow-up, 23,829 women (0.94%) were diagnosed with type 2 diabetes. The incidence of type 2 diabetes in women with UL (1.805/1,000 person-years) was higher than in those without UL (1.289/1000 person-years). In the multivariable-adjusted model, the hazard ratio for type 2 diabetes in women with UL was 1.216 (95% confidence interval [CI] 1.071-1.382), as compared to those without UL. Compared to women without UL, women with UL who did not undergo myomectomy had a risk 1.328 times (95% CI 1.143-1.542) higher for developing type 2 diabetes. Interestingly, women with UL who underwent myomectomy had no increased risk for developing type 2 diabetes. Conclusions: This study found that young women with UL are more likely to develop type 2 diabetes than those without UL. In addition, myomectomy seemed to attenuate the risk for developing type 2 diabetes in young women with UL.