Autoimmune polyglandular syndromes originally defined by Blizzard, Maclaren and Neufeld were classified into three constellations based on the clinical clustering of the various component diseases. Type I and type II are reasonably well circumscribed entities with type III being an ill-defined group. The autoimmune nature of these diseases has been based on the presence of lymphocytic infiltration in the affected gland, organ specific autoantibodies in the serum, cellular immune defects and an association with the HLA DR/DQ genes or immune response genes. Autoantibodies to the various endocrine and non-endocrine tissues not only offer a diagnostic clue to the autoimmune nature of diseases but also can be used to identify asymptomatic individuals who are at risk of developing other component diseases of the syndrome. In this review the clinical and serological spectrum of type I and II APS will be discussed.