Most of the swelling and pain outside the perineum after radiotherapy for cervical cancer is a normal reaction, while a small number of persistent swelling and pain should be considered as the possibility of lymphocyst formation. Radiotherapy for cervical cancer patients mostly chooses external abdominal irradiation or localized intravaginal irradiation, and different dosages and methods can be set to kill cancer cells according to patients’ individual conditions and tolerance level. However, radiation does not have a recognizable effect, and while it kills cancer cells, it also kills normal cells in the body. Patients may experience adverse reactions such as pain and swelling at the radiation site while undergoing radiation therapy. Swelling and pain in the vagina and perineum can be caused by cell edema and poor lymphatic reflux during radiation therapy for cervical cancer, which is a normal reaction. If the swelling and pain in the perineum persist and get worse, it is considered that lymphocysts may be formed, or the disease progresses when the radiation therapy is ineffective, so it is necessary to seek doctor’s help immediately, and improve the imaging examination to further evaluate the condition as instructed by the doctor.