To investigate the long-term outcomes of radioiodine therapy (RIT) for juvenile Graves’ disease (GD) and the ultrasonographic changes of the thyroid gland. All of 117 juvenile patients (25 males and 92 females aged 10 to 18 [median 16] years) who had undergone RIT for GD at our clinic between 1999 and 2018 were retrospectively reviewed. Each RIT session was delivered on an outpatient basis. The maximum I dose per treatment was 13.0 mCi, and the total I dose per patient was 3.6-29.9 mCi (median 13.0 mCi). I administration was performed once in 89 patients, twice in 26, and thrice in 2. Ultrasonography of the thyroid gland was regularly performed after RIT. The duration of follow-up after the initial RIT ranged from 4 to 226 (median 95) months. At the latest follow-up more than 12 months after RIT (n=111), the patients’ thyroid functions were overt hypothyroidism (91%), subclinical hypothyroidism (2%), normal (5%), or subclinical hyperthyroidism (2%). New thyroid nodules were detected in 9 patients, 4-17 years after initial RIT. Patients with newly detected thyroid nodules underwent RIT with lower doses of I, and had larger residual thyroid volumes than those without nodules. None of the patients were diagnosed with thyroid cancer or other malignancies during the follow-up period. Over a median follow-up period of 95 months (range 4-226 months) RIT was found to be effective and safe in juvenile GD. However, cumulative evidence from further studies are required to confirm the long-term safety of RIT for juvenile GD.