Autoimmune polyendocrine disorders are characterized by the presence of more than one autoimmune endocrine disease. Study of such disorders has provided unique insight into the pathogenesis of autoimmunity and the development of tolerance in the normal individual. Autoimmune polyendocrine syndromes I and II have distinctive inheritance patterns, genetic causes, component diseases, and implications for follow-up. Care for individuals with these diseases requires monitoring for additional autoimmune disorders and aggressive treatment of identified diseases to prevent morbidity and mortality in affected individuals.