Natural History Study of Children and Adults With Medullary Thyroid Cancer

* INCLUSION CRITERIA FOR PATIENTS: * Patients must have histologically or cytologically confirmed MTC, confirmed by the Laboratory of Pathology, NCI OR Confirmation of MEN2A or MEN2B diagnosis, regardless of presence of MTC. * Performance Status: Ability to travel to the NIH and to undergo evaluations to be performed on this protocol. * Informed Consent: Ability of patient or their legal guardian (if the patient is \<18 years old) to understand and willing to sign a written informed consent document. * Prior and current therapy: For the purpose of this study subjects who have not previously received medical or surgical treatment, patients, who have previously received medical or surgical treatment, and subjects who are currently receiving medical treatment and/or radiation for MEN 2 related manifestation(s) will be eligible. Prior and current treatment for MEN 2 related manifestations will be recorded at trial entry and throughout the study. * Patients must have a primary care provider (for example a primary oncologist or endocrinologist) who can provide and coordinate the medical care for the patient. EXCLUSION CRITERIA FOR PATIENTS: -In the opinion of the investigator the patient is not able to return for follow-up visits or obtain required follow-up studies. Inclusion Criteria for Parents or Primary Caregivers * Must be a parent or primary caregiver of a patient (\< 21) who has a histologically or cytologically confirmed MTC or who have MEN2 (regardless of MTC status). * Ability to understand and be willing to sign a written informed consent document. EXCLUSION CRITERIA FOR PARENTS OR PRIMARY CAREGIVERS: None