Autoimmune polyglandular syndrome is characterized by the coexistence of several autoimmune diseases, affecting predominantly the endocrine glands. Autoimmune polyglandular syndrome type III, as a subdivision of autoimmune polyglandular syndrome type II, is the co-occurrence of autoimmune thyroid disease with other autoimmune disorders without Addison disease. We present a rare case of autoimmune polyglandular syndrome type III in monozygotic twins. One of the twins also had autoimmune leukopenia. To our knowledge, leukopenia is the first mentioned coexistence in the literature of autoimmune polyglandular syndrome.