Autoimmune polyglandular syndrome type I (APS I) is an autosomal recessive disorder characterized by a combination of autoimmune manifestations affecting endocrine and non-endocrine organs. APS I usually presents in childhood. The three most common manifestations are chronic mucocutaneous candidiasis, hypoparathyroidism and Addison's disease. At least two of these must be present to fulfill the diagnostic criteria of this syndrome. The spectrum of other associated diseases includes gonadal insufficiency, alopecia, vitiligo and chronic active hepatitis. APS I is caused by a mutation in the AIRE-gene (autoimmune regulator) located on chromosome 21. Analysis of specific autoantibodies against intracellular enzymes, particularly enzymes in the synthesis of steroids and neurotransmittors, can be used in the diagnosis of APS I and to predict different manifestations of the disease.