Incidental/therapeutic thyroid irradiation causes hypothyroidism and nodular disease. As increasing numbers of children, adolescents and young adults are being cured of cancer after being treated with radiation therapy that has included the thyroid bed, it is important to understand whether early diagnosis and treatment of any radiation-related thyroid changes has an impact on their evolution and outcome. In this review the authors discuss main epidemiologic data, morbidity events, radiation cancerogenic effects and also original data about patients surveillance and evolution control of iatrogenic effects, together with some experiences of prospectively reducing the occurrence of post-radiation hypothyroidism.