Importance Medullary thyroid cancer (MTC) is a relatively rare neoplasm of the thyroid but accounts for 14% of thyroid cancer–related deaths. Female sex, young age, and stage at presentation have been found to predict survival and treatment. However, patterns of survival and treatment by socioeconomic status and race/ethnicity have not been fully described. Objective To determine whether socioeconomic status and race/ethnicity are associated with survival and treatment in patients with MTC.