Insulin-dependent diabetes mellitus is an autoimmune disease the development of which is influenced by genetic factors (Cahill & McDevitt, 1981). As concordance for IDD is less than 50% in identical twins, environmental factors are also required for the development of IDD. Although viral agents have been implicated in the past, the specific environmental components leading to IDD remain unknown. This paper reviews current research focused on the genetic factors that influence susceptibility to IDD.