This case study is available in English. It is intended for advanced level health care providers to help aid them in the evaluation of potentially exposed patients. This case study provides information related to at risk populations including peds, exposure pathways, physiologic effects, clinical evaluation, treatment and management, as well as workplace and environmental standards and regulations of radiation exposure from I-131. Upon completion of this case study the participant should be able to describe the major sources of I-131 in the environment, identify the major routes of human exposure, describe the population group most at risk for health effects from past exposure to I-131 and why, describe the four factors contributing to the internal dose of I-131 contamination, assess a patient's environmental or occupational exposure to I-131, describe the diagnostic evaluation of a thyroid nodule in an individual exposed to I-131, list two important actions to take if an environmental release of I-131 occurs, discuss indications for prophylactic use of potassium iodine (KI) after an I-131 exposure, and list three sources of information one could access if an I-131 release occurs. The CDC designates this educational activity for a maximum of 2.25 hours toward the American Medical Association (AMA) Physician's Recognition Award, 2.5 contact hours in nursing, and 0.2 Continuing Education Units (CEUs).