A 58-year-old woman who presented with inguinal hernia for the first time was diagnosed as seminoma and complete androgen insensitivity syndrome (CAIS). The patient received a late diagnosis, and therefore she could not take a proper management. CAIS is a rare X-linked recessive disease with an XY karyotype that is caused by androgen receptor defects. It usually present with primary amenorrhea or inguinal hernia. The risk of malignant transformation of undescended testis increases with age, thus gonadectomy should be performed after puberty. We present a case of large advanced seminoma in a woman with CAIS who was neglected and diagnosed lately.