The retrospective analysis of the case files of children with differentiated thyroid carcinoma (DTC) was performed to define the disease by its presentation, clinical course and outcome of radioiodine therapy.Between 1967 to October 2002, 1754 patients with thyroid cancer were treated in the Dept of Neuclear Medicine, AIIMS, out of which 122 (7%) were < or = 20 years of age (71 girls and 51 boys). The mean age was 15.8 +/- 3.6 years and the mean duration of follow-up was 90 +/- 59.3 months. Mean tumor size was 4.4 cm. Histologically, 85% of the patients had papillary and rest follicular carcinoma. Cervical lymph node involvement was seen in 64%, and distant metastases, mainly pulmonary, in 23% of the patients. The presentation of the disease was very aggressive in the first decade of life with male preponderance. All but one patient in this age group had nodal and/or distant metastases; in 83.3% the disease had spread to the lymph nodes and 67% had metastases to the lungs. The post-surgery 48-hour mean radioiodine neck uptake was 10.5 +/- 7.6%.94% of the residual thyroid, 88% of nodal metastases and 71% of pulmonary metastases were ablated requiring mean cumulative doses of 2.8 +/- 2.7 GBq, 4.5 +/- 2.7 GBq and 10.4 +/- 7.9 GBq of 131I, respectively. Average number of doses required for remnant, nodal and pulmonary metastases ablation were 1.3, 2.2 and 3.3, respectively. 80% of the patients with only remnant thyroid tissue and 50% with cervical lymph node metastases got ablated with a single dose of 131I. Overall, 87% patients were currently free of disease. While, nine patients had nodal recurrence between surgery and radioiodine treatment, no recurrence was observed thereafter and 3 disease related deaths producing overall mortality of 2.5% (all in children < or =10 years of age) were seen in the mean follow-up of 7.5 years.Differentiated thyroid cancer in children and adolescents is rare but aggressive. The biological behavior differs from that in adults and is related to the age. Younger the age (< or =10 years), more aggressive and widespread is the disease with male preponderance and high mortality. The post-surgical radioiodine ablation/therapy is an important and effective adjuvant in the management of DTC in children and adolescents and even though they present with advance disease, long-term survival and overall prognosis is good.