The incidence of thyroid cancer in childhood amounts to approximately 0,5/100.000/year. However, after exposure to ionizing irradiation, the incidence may increase more than 20 fold. In children, lymph node metastases of differentiated thyroid cancer are frequent (more than 50%); distant metastases mainly to the lung are seen in 20-30%. The method of choice for the primary diagnosis of thyroid cancer today is ultrasonography with 7,5 - 10 MHz probes, accompanied by fine-needle aspiration biopsy. Differentiated thyroid cancer has to be treated with a multidisciplinary approach comprising total thyroidectomy and lymph node dissection, post-operative radioiodine treatment and TSH-suppression by levothyroxine. The long-term results of this treatment approach are generally good with 10-year survival rates of 95% and higher. The treatment of children with disseminated pulmonary metastases however, may be complicated due to the increased risk of the induction of pulmonary fibrosis by radioiodine.