Research goals: The aim of this research is to determine the incidence of thyrotoxicosis in the population of children and adolescents treated in the County of Split-Dalmatia. Another goal is to analyze and determine if there is a distinction in the prevalence of thyrotoxicosis, considering the patient’s age and gender. Also there is a need to inspect the remission and relapse percentage of thyrotoxicosis among the patients younger than 18 years. At last, the goal is to define the indications and period for the medical treatment of hyperthyroidism with a radioiodine therapy or a surgical procedure. Materials and methods: All the data used for this diploma thesis are collected from the Clinic for Pediatric Medicine of CHC Split. The medical diagnosis for thyrotoxicosis is based upon the anamnesis, physical examination, thyroid ultrasound, serum concentrations of thyroid hormones (T3, T4, TSH) and TSH receptor antibodies (TRAb). At least 80 patients were detected with the diagnosis of hyperthyroidism. The patient data are presented in tables (Excel, version, city, country) and in addition, the descriptive statistical analysis of collected data has been conducted and displayed Results: During the period between 2002 and 2019 there were 80 patients with the diagnosis of thyrotoxicosis. The female to male ratio is 4:1, which corresponds to the information from other literature sources. The incidence of Graves disease in the County of Split-Dalmatia is estimated of 3.2/100 000. Around 70% of patients were diagnosed with Graves disease (GD), while 26% of them with Hashimoto disease. The diagnosis is based upon the anamnesis, clinical examination, ultrasound and analysis of TRAb antibodies. All the children with GD were treated with thyrostatic drugs (TS) and adrenergic blocking agents. Looking at patients with Hashimoto disease, 18.4% of them were treated with TS therapy, while 38% were treated with adrenergic blocking agents as well. The remission was attained in 26.7% of patients with GD after 6 to 63 months of treatment with tyrostatic drugs. That data corresponds to the clinical experience from other hospital centers. For example, a study conducted in Argentina shows that from 113 patients that had TS therapy for 10 years, 33% of them were in remission (32), while in Japan, out of 723 patients with GD, 46.2% of them were in remission approximately after 3.8 years of taking TS drugs (33). Relapse of GD in 38 Croatian patients was recognized in 40% of the cases, which is a slight decrease compared to published study results. Conclusion: We demonstrated that female children are 4 to 5 times more likely to have hyperthyroidism than boys. Also, we proved that the remission of Graves disease depends on multiple factors such as the thyroid size, level of TRAb and age, thus the youngest patients are less likely to be in remission compared to adults. Thyrostatic drugs (TS) should be used as the drug of choice, but if we decide for the definite treatment, a surgical procedure should be chosen over the radioiodine therapy, since the latter causing the higher risk of development of a malignant disease. To conclude, it is important to encourage the parents of the patients with little probability to be in remission to decide faster.