The majority of people with thyroid cancer have no known risk factors. As a result, it is not possible to prevent most cases of the disease. Familial medullary thyroid carcinoma (FMTC) is one exception. With the development of genetic blood testing, most cases of FMTC can be prevented. After the disease is identified in a family, all family members should be tested for RET mutations. These tests may include blood chemistry tests and more complicated genetic tests. Those who test positive for RET mutations of FMTC can have surgery to prevent the disease, even if they do not have thyroid nodules or any other symptoms of thyroid cancer.

Some physicians believe the increase in cases of thyroid cancer may result from x-ray testing of young children. Although a solid connection has not been proven, parents may want to avoid unnecessary x-ray testing of their children.