Autonomously functioning thyroid nodules (AFTNs) in children and adolescents (under age 18) are unusual but are not as rare as earlier reports suggested. These lesions have a significantly different biologic potential than similar lesions in older patients. In the younger age group there is a more rapid progression toward toxicity and a higher incidence of thyroid carcinoma. Our experience with 12 patients is combined with those previously reported for identification of a total of 61 children and adolescents with AFTNs, of whom 53 have undergone operation. Hyperthyroidism was present in 15 patients (24.6%), and in six patients (11.3%) the AFTN was due to a well-differentiated thyroid carcinoma. Surgical treatment is advisable for all children and adolescents with AFTNs because of the risks of hyperthyroidism and thyroid carcinoma. Surgical excision (lobectomy is preferred) results in rapid restoration of a euthyroid state for the toxic AFTN and allows histopathologic diagnosis. Therapy with radioiodine is not advisable for treatment of AFTNs in this age group. Thyroid-stimulating hormone suppression should be used for all patients with a diagnosis of thyroid carcinoma.