A 29-year-old female patient who was being followed up for differentiated papillary thyroid carcinoma was referred to us for exploration of any possible metastasis since her serum thyroglobulin levels were high. The patient underwent an F-18 fluorodeoxyglucose positron emission tomography study, and a pathologically increased FDG uptake at the left lower abdomen was detected corresponding to a solid, cystic lesion on CT images. The patient had a history of primary amenorrhea and, together with the magnetic resonance imaging findings of absent uterus, short and blind end vagina, a diagnosis of androgen insensitivity syndrome was made. The patient underwent laparoscopic left pelvic mass resection, and the histopathology of the lesion revealed Sertoli-Leydig cell tumor.