Autoimmune diabetes is characterized by inflammatory infiltration; however, the initiating events are poorly understood. We found that the islets of Langerhans in young nonobese diabetic (NOD) mice contained two antigen-presenting cell (APC) populations: a major macrophage and a minor CD103⁺ dendritic cell (DC) population. By 4 weeks of age, CD4⁺ T cells entered islets coincident with an increase in CD103⁺ DCs. In order to examine the role of the CD103⁺ DCs in diabetes, we examined Batf3-deficient NOD mice that lacked the CD103⁺ DCs in islets and pancreatic lymph nodes. This led to a lack of autoreactive T cells in islets and, importantly, no incidence of diabetes. Additional examination revealed that presentation of major histocompatibility complex (MHC) class I epitopes in the pancreatic lymph nodes was absent with a partial impairment of MHC class II presentation. Altogether, this study reveals that CD103⁺ DCs are essential for autoimmune diabetes development.