We present a case report of a 14-year-old girl with Schmidt’s syndrome, also known as autoimmune polyglandular syndrome type 2. The previously healthy child began experiencing symptoms including weight loss, nausea, abdominal pain, and poor exercise tolerance. Symptoms worsened during infections, resulting in multiple hospitalisations at a district hospital. During one hospitalisation, autoimmune thyroiditis was diagnosed, and levothyroxine therapy was initiated. After starting levothyroxine treatment, the patient's condition deteriorated, and episodes of syncope appeared. She was admitted urgently to the Department of Paediatric Endocrinology and Rheumatology, where primary adrenal insufficiency was diagnosed, and autoimmune thyroid disease was confirmed, constituting the two main components of Schmidt’s syndrome. Hydrocortisone treatment was initiated, followed by levothyroxine therapy after three days. It should be remembered that patients with autoimmune thyroiditis may have other coexisting autoimmune diseases, including life-threatening adrenal insufficiency.