Pelvic inflammatory disease (PID) refers to infection of the uterus, fallopian tubes, and adjacent pelvic structures that is not associated with surgery or pregnancy. PID causes major medical, social, and economic problems worldwide. Long-term sequelae, most notably tubal factor infertility and ectopic pregnancy, are common and extremely costly to the healthcare system. The most important causative micro-organisms are Chlamydia trachomatis, Neisseria gonorrhoeae, and micro-organisms associated with bacterial vaginosis. The clinical spectrum of PID ranges from subclinical endometritis to severe salpingitis, pyosalpinx, tubo-ovarian abscess, pelvic peritonitis, and perihepatitis. Clinical diagnosis of PID has limitations. The clinical diagnostic criteria are insensitive and nonspecific, and false-positive and false-negative diagnosis is common; however, direct visual diagnosis is not always feasible, requires general anesthesia, and is costly. More research is needed of noninvasive diagnosis of PID. Current treatment guidelines call for broad-spectrum antimicrobial coverage. Screening for asymptomatic chlamydial infection is the mainstay of prevention of PID. Emerging evidence from randomized controlled trials provides strong evidence that intervention with selective screening for chlamydial infection effectively reduces the incidence of PID.