Pelvic inflammatory disease (PID) is the most serious complication of sexually transmitted infections (STIs, also known by the older name of sexually transmitted diseases or STDs) such as chlamydia and gonorrhea.
PID affects the upper genital tract including the uterus, ovaries, and fallopian tubes. Well over a million women get PID each year in North America. It's the leading cause of tubal infertility in young women, but it can usually be prevented if STIs are detected and treated early. One of the long-term consequences of PID is chronic pelvic pain.