Autoimmune diseases and sarcoidosis may be related and, especially, the association between sarcoidosis and autoimmune thyroid disease has long been recognized. The frequency and type of endocrine autoimmunity was examined in a series of Swedish patients with sarcoidosis. Of all patients (N = 89) with documented sarcoidosis attending the Department of Pulmonary Medicine between January 1980 and December 1991, 78 patients (44 males and 34 females; median age at the time of the study 48 years. range 22-81 years) were examined at the Department of Endocrinology, Malmö University Hospital, in the present study. Fifteen patients (19.2%) had clinical or serological evidence of endocrine autoimmunity. Two patients had Addison's disease, both with polyglandular autoimmune (PGA) syndrome type II: evidence of thyroid autoimmunity was found in 13 patients, eight with clinical autoimmune thyroid disease (ATD) (two with Graves' disease and six with autoimmune thyroiditis), of whom two had PGA syndrome type III, and five with isolated positive thyroid serology; two patients had insulin-dependent diabetes mellitus and one had premature ovarian failure. The frequencies of Addison's disease, clinical ATD and PGA syndrome type II were significantly higher compared with the frequencies found in the general population. In conclusion, a high frequency of endocrine autoimmunity in patients with sarcoidosis, occurring in about 20% of the cases, was demonstrated. Thyroid autoimmunity and polyglandular autoimmune syndromes occurred most frequently. Complex immunological and genetic mechanisms might explain the association of sarcoidosis and endocrine autoimmune diseases.