As the last extensive series of patients with Addison's disease and coincident autoimmune phenomena were published approximately two decades ago, we studied the cause of the disease, the prevalence of autoimmune disorders and the frequency of occurrence of autoantibodies in 91 patients (31 men and 60 women, mean age 45.3-years-old, range 12-77) with Addison's disease. The cause of Addison's disease in six patients was tuberculosis (6.6%), and autoimmune adrenalitis was considered to be the cause in 83 patients (91.2%). In two patients (2.2%) other causes were responsible for Addison's disease. In 47% of the patients with autoimmune Addison's disease at least one other autoimmune disorder was present. Primary hypothyroidism had the highest prevalence (20.5%), followed by vitiligo (9.6%), non-toxic goiter (8.4%), premature menopause (7.3% of the women), Graves' disease (6%), pernicious anaemia (4.8%), Sjögren's disease (2.4%), hypoparathyroidism (1.2%), type 1 diabetes mellitus (1.2%) and coeliac disease (1.2%). The frequency of autoantibodies in the patients with autoimmune Addison's disease was: adrenal antibodies (82.7%), antibodies against microsomal antigens (58%), thyroglobulin antibodies (23.4%), parietal cell antibodies (19.8%), pancreatic islet cell antibodies (6.2%) and ovary antibodies (3.7% of the women). In comparison with other extensive series of patients with Addison's disease, we found the highest prevalence of autoimmune adrenalitis as the cause of Addison's disease, the highest prevalence of hypothyroidism and vitiligo as concomitant autoimmune disorders and the lowest prevalence of type 1 diabetes mellitus.