The treatment of hypothyroidism and hyperthyroidism is briefly reviewed. L-T4, which is the treatment of choice of hypothyroidism, should be administered once daily after an overnight fast at the dosage of 10-12 mg/kg/day in newborns and of 100 mg/m2 in older children. FT4 and TSH serum levels will normalize within few weeks from the beginning of treatment and should be maintained in the normal range thereafter by appropriate increases of the dosage during growth. The first choice treatment in children with hyperthyroidism due to Basedow disease is the administration of antithyroid drugs, i.e. methimazole at the initial dosage of 0.4-0.6 mg/kg/day b.i.d. or t.i.d.; after remission, the dosage of this drug can either be reduced or L-T4 added in order to avoid hypothyroidism. Treatment should be continued for at least 24 months and the patient followed thereafter to detect possible relapses. Side effects are rare, the most frequent are skin rashes and the most severe is agranulocytosis, so complete blood count should be evaluated frequently especially in the first months of treatment. Surgery (total or near-total thyroidectomy) should be considered in case of failure of medical therapy, even if radioiodine administration, used until now mainly in adults, is gaining favour also for children especially in the United States.