Pelvic inflammatory disease (PID) is an infection of the reproductive organs in women. The pelvis is located in the lower abdomen and includes the fallopian tubes, the ovaries, the cervix, and the uterus. Several different types of bacteria can cause PID, including the same bacteria that cause the sexually transmitted infections (STIs) gonorrhea and chlamydia. What commonly occurs is that bacteria first enter the vagina and cause an infection. As time passes, this infection can move into the pelvic organs. Some women with pelvic inflammatory disease do not have symptoms. For the women who do have symptoms, these can include: pain in the lower abdomen (the most common symptom) pain in the upper abdomen fever painful sex painful urination irregular bleeding lower back pain vaginal discharge tiredness