Autoimmune polyendocrinopathy - candidosis - ectodermal dystrophy (APECED), also known as autoimmune polyendocrine/polyglandular syndrome type 1 (APS1), is a rare disease caused by mutations in the autoimmune regulator (AIRE) gene pair resulting in absence of active AIRE protein, which is essential for both central and peripheral self-tolerance. The phenotype is widely variable. Apart from the classical triad of mucocutaneous candidosis, hypoparathyroidism and adrenal failure, several other components, some of which are potentially life-threatening, may develop. Due to the unpredictable clinical course, the patients need regular follow-up by a clinician familiar with the disease. Diagnosis is often possible by clinical diagnostic criteria, but in many cases the early clinical picture does not bring it to mind. A novel tool, search for autoantibodies against interferon-omega, enables proof or exclusion of APECED with more certainty than gene analysis. It is highly specific and sensitive for APECED if thymoma and myasthenia gravis are excluded.