In recent years our knowledge on thyroid diseases in childhood has been increased. Several forms of congenital hypothyroidism (dysgenesis, dyshormongenesis, thyrotropin resistance and some central forms) are consequences of gene mutations. Maternal hypothyroxinemia due to severe iodine deficiency leads to early neurological damage and congenital hypothyroidism. Neonatal screening of congenital hypothyroidism and early treatment with l-thyroxin ensure good prognosis. Differential diagnosis of the various forms of congenital hypothyroidism in newborns is not an easy task. The need for treatment of transient hypothyroxinemia is still controversial. Diagnosis of juvenile lymphocytic thyroiditis can be ascertained by the clinical status, ultrasound examination, detection of anti-peroxydase antibodies, evaluation of thyroid function, and fine needle aspiration cytology. L-thyroxin therapy is recommended in cases of subclinical and manifest hypothyroidism. The transient form of the rare newborn hyperthyroidism is the consequence of maternal Graves-Basedow disease. It can be a sever condition and its permanent form is caused by TSH-receptor gene mutation. In the pathogenesis of autonomic thyroid adenoma mutations of the TSH-receptor and the alpha subunit of the stimulatory G-protein are involved. Treatment of Graves-Basedow disease in childhood is a debated question. The first choice is medical treatment with antithyroid and beta-blocking drugs. However, remission rate is low under this therapy, and the disease is characterised by frequent relapses. For this reason, the necessity of definitive therapy frequently arises. In Europe subtotal thyroidectomy is used as second choice of therapy, but clinical experience in the United States showed that radioiodine treatment is a safe and effective therapy for children and adolescents. Iodine deficient goitre in childhood is a form of iodine deficiency disorder. It is the consequence of adaptation to iodine deficiency. It can be treated by iodine or/and l-thyroxin, and its development can be prevented by iodinated salt. In childhood, thyroid nodule needs for a detailed investigation because of the possibility of thyroid cancer. Medullar thyroid carcinoma indicates genetic screening in the patients and their family, and the presence of disease-causing RET-proto-oncogene mutation confirms the need for total thyroidectomy already in childhood.