Type 1 diabetes mellitus (T1DM) is a chronic disease characterized by hyperglycaemia secondary to absolute insulin deficiency. It is the result of T cell-mediated autoimmune destruction of the insulin-producing β-cells that reside in the islets of Langerhans. T1DM is associated with circulating autoantibodies to β-cell antigens. It results from an interplay between genetic and environmental factors. The autoimmune process can start in infancy, and the rate of autoimmune β-cell destruction varies widely between individuals.