Abstract The International Diabetes Federation estimates that approximately 0.4% of the Belgian population is diagnosed with type 1 diabetes mellitus, which is similar to other industrialized countries. The prevalence of transgenderism is estimated at 0.6% to 0.7% of all adults in Western populations. In this study, we evaluated whether there was an increased prevalence of type 1 diabetes mellitus in transgender people in the local cohort. Medical records of transgender patients were analyzed retrospectively. From January 1, 2007 until October 10, 2016, 1,081 transgender patients presented at a tertiary reference center to start hormonal treatment. Nine of these 1,081 patients were previously diagnosed with type 1 diabetes mellitus and 1 was diagnosed with latent autoimmune diabetes in adults. A 2.3-fold higher prevalence of type 1 diabetes mellitus was observed in transgender patients. We concluded that type 1 diabetes mellitus was more prevalent in transgender patients than one would expect from population prevalences. This could be a spurious result in a local cohort, because a causal relation seems unlikely, but our finding might encourage other centers to investigate this putative association. Defreyne J, De Bacquer D, Shadid S, et al. Is Type 1 Diabetes Mellitus More Prevalent Than Expected in Transgender Persons? A Local Observation. Sex Med 2017;5:e215–e218.