An 80-year old female presented with a well-defined tumor of the anterior middle neck, and a diagnosis of thyroglossal duct cyst was made. When the tumor size increased, malignancy was suspected. Ultrasonography revealed a smooth, heterogeneously hypoechoic area at her anterior neck. Contrast-enhanced computed tomography showed a well-defined contrast-enhanced tumor inferior to the hyoid bone. Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) showed a fluorine-18 fluorodeoxyglucose-avid tumor with a maximum standardized uptake value of 12.8. Surgical tumor resection was performed, and the histopathological finding was ectopic papillary carcinoma lacking thyroglossal duct remnants, which is very rare. To our knowledge, few cases of ectopic thyroid carcinoma with 18F-FDG PET/CT findings have been reported. Ectopic thyroid carcinoma lacking thyroglossal duct remnants should be considered a differential diagnosis in cases of 18F-FDG uptake in an anterior middle neck tumor.