This is a clinical practice guideline for patients who are Rearranged during Transfection (RET) proto-oncogene mutation carriers. The guideline provides recommendations on the timing and extent of thyroid surgery. Recommendations are stratified by patient risk with considerations made to genetic characteristics, patient age at diagnosis, and calcitonin levels at the time of decision making. Postoperative management and follow-up is also discussed. Outcomes of interest include risk of metastasis and risks of extended surgery (including permanent hypoparathyroidism and permanent paralysis of the recurrent laryngeal nerve).