Autoimmune Addison's disease (AAD) is the main reason of primary adrenal failure. More than a half of patients display additional autoimmune conditions, which represent a considerable clinical concern. This study aimed to investigate the prevalence of concomitant autoimmune disorders in 85 Polish AAD patients (61 females, 24 males). Mean age at AAD onset was 34.6 ± 12.6 years, significantly earlier in males (P < 0.001). Sixty-nine patients presented positive serum antibodies to 21-hydroxylase and shorter AAD duration than those with negative results (P = 0.027). Seventy-three subjects suffered from coexisting autoimmune disorders. Serum autoantibodies against thyreoperoxidase, thyroglobulin, TSH receptor, glutamic acid decarboxylase, insulin, tyrosine phosphatase-like protein IA2, parietal cell H(+)/K(+)-ATPase, intrinsic factor and tissue transglutaminase were detectable in 71.8, 41.2, 4.7, 21.0, 4.9, 2.5, 49.4, 12.0 and 3.5% of patients, respectively. Antinuclear antibodies were found in 12.5%. Thyroid autoimmunity was most common (46 subjects with lymphocytic thyroiditis, 19 with Graves' disease), followed by atrophic gastritis (29.4%), pernicious anaemia (11.8%), hypergonadotropic hypogonadism (8.2%), vitiligo (8.2%), type 1 diabetes (7.1%), celiac disease (3.5%) and alopecia (2.4%). Gender differences were observed only for thyroid autoimmunity. Current study confirms particular tendency of AAD patients to develop other autoimmune disorders. Active search for concomitant conditions is warranted to prevent serious complications.