Papillary thyroid carcinoma frequently metastasizes to regional lymph nodes. However, cervical lymph node metastasis as a sole manifestation of occult papillary thyroid carcinoma is rarely observed. Ectopic thyroid is an uncommon condition defined as the presence of thyroid tissue at a site other than pretracheal area. Approximately 1-3% of all ectopic thyroid tissue is located in the lateral neck. This entity may represent the only functional thyroid tissue in the body. Malignant transformation of ectopic thyroid is uncommon; but even rarer is the development of papillary carcinoma on it. We present a case of a 33-year-old man with an incidental lateral neck mass diagnosed after a motor vehicle accident. Total thyroidectomy and lymph node resection were completed without evidence of papillary thyroid carcinoma. Malignant transformation of heterotopic thyroid tissue was the final diagnosis. The possibility of an ectopic thyroid cancer should be considered in the differential diagnosis of a pathological mass in the neck. The uniqueness of this case strives in the rarity that the thyroid gland was free of malignancy, despite ectopic tissue being positive for thyroid carcinoma. Management strategies, including performance of total thyroidectomy, neck dissection, and treatment with radioiodine, should be based on individualized risk assessment.