Pelvic inflammatory disease (PID) is an infection and inflammation of the uterus, ovaries, and other female reproductive organs. It causes scarring in these organs. This can lead to infertility, ectopic pregnancy, pelvic pain, abscesses, and other serious problems. PID is the most common preventable cause of infertility in the United States. Gonorrhea and chlamydia, two sexually transmitted diseases, are the most common causes of PID.