An increased incidence of thyroid cancer in the exposed children remains the most well-documented long-term effect of radioactive contamination after the Chernobyl nuclear accident in April, 1986. Multiple studies on approx 4000 children and adolescents with thyroid cancer have provided important new information about the epidemiological, clinical, pathological, and molecular aspects of radiation-induced carcinogenesis in the thyroid gland. They revealed that environmental exposure to 131I during childhood carries an increased risk of thyroid cancer and the risk is radiation dose dependent. The youngest children are most sensitive to radiation-induced carcinogenesis, and the minimal latent period for thyroid cancer development after exposure is as short as 4 yr. The vast majority of these cancers are papillary carcinomas, many of which have characteristic solid or solid-follicular microscopic appearance. On the molecular level, post-Chernobyl tumors are characterized by frequent occurrence of chromosomal rearrangements, such as RET/PTC, whereas point mutations of BRAF and other genes are much less common in this population.