The authors here report a 54-year-old (gravida 0, para 0), who claimed to have had her menarche at age 13 and menopause at 52 years. Two months prior to presentation, the subject first noticed a hard but elastic fist-sized mass in the left inguinal region that gradually grew, causing pressure-related pain. Although the external genitalia appeared female, the vagina was short and blind-ending, and no uterus or ovaries were identified on transvaginal ultrasound. Chromosome banding results (G-band method) showed 46XY. Laparoscopy revealed no traces of a vestigial uterus or ovaries; thus, based on the appearance of the external genitalia, a diagnosis of testicular feminization syndrome was made. Pathological testing of the palpable mass led to a diagnosis of seminoma with Leydig cell hyperplasia. Thus, in this case, the development of a seminoma in an undescended testis led to the detection of testicular feminization syndrome.