Ultrasonography (US) and radionuclide thyroid scanning are the imaging modalities of choice in the evaluation of the thyroid gland in children. The main normal US patterns of the thyroid gland are reviewed. In early infancy, thyroid imaging is usually performed in the context of congenital hypothyroidism (CH). The aetiological diagnosis of CH is usually based on the combined use of US and radionuclide thyroid scanning. A detailed description of thyroid abnormalities observed in CH is given. Thyroid dysgenesis includes athyreosis, 'empty' thyroid area with ectopic thyroid tissue and thyroid hypoplasia (global hypoplasia and thyroid hemiagenesis). Mild thyroid developmental anomalies (pyramidal lobe, thyroglossal duct cysts, thyroid hemiagenesis) may be observed in euthyroid patients or among first-degree relatives of a CH population with thyroid dysgenesis. A normally located gland (goitre, normal-sized thyroid gland or hypoplastic thyroid gland) may also be observed in patients with CH. The main patterns observed in chronic and acute thyroiditis, in hyperthyroidism and thyroid tumours are described. Moreover, fetuses and neonates born to mothers with Graves' disease are at risk of thyroid dysfunction and goitre due to hypothyroidism in relation to excessive maternal treatment or to maternal hyperthyroidism which may be observed with fetal US.