A case of polyglandular autoimmune syndrome (PGA) in a 14-year-old boy presented is. The case syndromes included hyperthyreosis with a high titre of antithyreoglobulin and antimicrosomal antibodies and hypofunction of adrenal glands confirmed by the test with ACTH. The boy was admitted to the clinic in an average general condition. Marked insufficiency of the body mass in comparison to the height, many pigmented moles on the skin and features of thyroid hyperfunction confirmed by laboratory examinations were observed. Thyreostatic and b-blocker were applied for treatment. The boy was discharged in the condition of clinical and biochemical euthyreosis. After two months of follow-up in the Endocrinologic Outpatient Department there was no weight gain, no appetite and general weakness. The anamnesis showed multiple faintings. The boy was hospitalized again. Suspecting adrenal hypofunction, a test with ACTH was carried out but it did not give any result. Substitutive treatment was applied resulting in a gradual improvement of the general condition and disappearance of complaints. The case is presented due to the rare incidence of the syndrome and due to the diagnostic difficulties.