A review of 295 patients with autoimmune Addison's disease which occurred as part of a polyglandular autoimmune syndrome is presented. Information of 41 cases was obtained from our clinics and from the examination of medical records, while 254 cases were culled from the literature. We report that autoimmune Addison's disease in association with other autoimmune diseases occurs in at least two distinct types. Addison's disease occurring in Type I polyglandular autoimmune disease (PGA) is associated with chronic mucocutaneous candidiasis and/or acquired hypoparathyroidism. The age of onset is predominately in childhood or in the early adult years. Type I PGA syndrome is also frequently associated with chronic active hepatitis, malabsorption, juvenile onset pernicious anemia, alopecia and primary hypogonadism. Insulin requiring diabetes and/or autoimmune thyroid disease are infrequent. In contrast, Addison's disease in Type II PGA is associated with insulin requiring diabetes and/or autoimmune thyroid disease(s). Although the age of onset of Addison's disease in Type II PGA syndrome is not confined to any age group or any specific sex, it occurs predominately in the middle years of life in females. The associated autoimmune diseases found in Type I disease, such as chronic active hepatitis, etc. (see table II) are rare in Type II PGA disease except for a low frequency of gonadal failure. We provide evidence to support the concept that the Addison's diseases in Type I and II PGA syndromes have different genetic bases, as related to HLA haplotypes, and possibly have different underlying pathogeneses.