Type 1 diabetes mellitus (T1DM) is an autoimmune disease that involves the progressive destruction of the insulin‑producing beta cells in the islets of langerhans. It is a complex process that results from the loss of tolerance to insulin and other beta‑cell‑specific antigens. Various genetic and environmental factors have been studied so far, but precise causation has yet to be established. Numerous studies in rodents and human subjects have been performed in order to elucidate the role of B and T cells, which determine the risk of development and progression of diabetes. These studies have demonstrated that while T1DM is fundamentally a T‑cell‑mediated autoimmune response, the development of this disease results from complex interactions between the adaptive and innate immune systems, with numerous cell types thought to contribute to pathogenesis. Like any complex disease, the variation in severity and incidence of T1DM can be attributed to a combination of genetic and environmental factors.