Background and aims Patients with Grave`s disease are more likely to develop type 1 diabetes, than general population. In children are rare cases in which hyperthyroidism precede diagnosis of type 1 diabetes.

Methods We described a case of two autoimmune conditions – type 1 diabetes and Grave`s disease being diagnosed at the same patient.

Results A 15 year old boy shows about two months ago palpitations, tremor, anxiety, swelling at the base of the neck. He had also experienced weight loss of approximately 7 kg over the past 2 months. It shows the endocrinologist who performs thyroid ultrasound and other lab investigations, and diagnose the patient with thyrotoxicosis, for which he was started on Methimazole 30 mg/day and Propranolol 60 mg/day. After a month of treatment, symptoms persist, adding the last 2 weeks polyuria and polydipsia, for which presents in our clinic. On physical examination he was cashectic, anxious, restless, slightly tremor of the extremities. His pulse rate was 115 bpm, in sinus rhythm and his blood pressure was 126/68 mmHg. Neck examination revealed a diffusely enlarged goitre. Based on symptoms, physical examination and laboratory tests (antiglutamat decarboxylase (GAD-II) antibodies and anti-insulin antibodies – positive, HbA1c- 6.5%, serum glucose level at admission=204 mg/dl) he was diagnosed with type 1 diabetes. Further blood tests taken at the time of admission showed a level of thyroid-stimulating hormone of 0005 uUI/ml, free thyroxine (fT4) of 3.75 ng/dl (0.7–1.63) anti-thyroid peroxidase antibodies positive( ATPO), thyroid stimulating hormone receptor antibody(TRab) also positive. Celiac screen was negative.

Conclusions There is little certainly evidence regardind the role of thyrotoxicosis in development diabetes. Signs and symptoms of hyperthyroidism may mask a latent onset of diabetes. Reaching euthyroid state can improve glicemic control, as well as treating diabetes makes easier to control hyperthyroidism.