A 10-YEAR-OLD GIRL underwent reduction cheiloplasty and excision of tongue nodules. The development of progressively patulous lips and thickening of the tongue began at age 6 years. Following surgery, a right neck mass was discovered. Thyroid scan revealed an enlarged gland with a cold area in the upper two thirds of the right lobe. A right thyroidectomy was performed. Her medical history included abdominal distension and the onset of severe constipation at age 4 years, which responded to medical treatment. On physical examination thick lips and an enlarged, nodular tongue were present (Figure 1 and Figure 2). A firm, visibly enlarged goiter was palpable in the left thyroid gland. An ultrasound study demonstrated an enlarged left lobe of the thyroid with 2 hypoechoic nodules and bilateral, enlarged cervical lymph nodes. Her serum calcitonin level was 299 pmol/L (reference, <26.6 pmol/L). A total thyroidectomy was performed with modified radical neck dissection. Pathologic interpretation of the removed tissue revealed medullary thyroid carcinoma (MTC) with metastases to the cervical lymph nodes. A review of the tongue biopsy specimen was consistent with mucosal neuromas. DNA sequencing analysis of exon 16 of the RET proto-oncogene from peripheral blood cells showed a germline M918T mutation (Figure 3).