Pelvic inflammatory disease (PID) is an infection of the upper genital tract in women that can include endometritis, parametritis, salpingitis, oophoritis, tubo-ovarian abscess, and peritonitis. The spectrum of disease ranges from subclinical, asymptomatic infection to severe, life-threatening illness; sequelae include chronic pelvic pain, ectopic pregnancy, and infertility. PID is diagnosed clinically, with laboratory and imaging studies reserved for patients who have an uncertain diagnosis, are severely ill, or do not respond to initial therapy. The Centers for Disease Control and Prevention diagnostic criteria include uterine, adnexal, or cervical motion tenderness with no other obvious cause in women at risk of PID. Empiric treatment should be initiated promptly and must cover Chlamydia trachomatis and Neisseria gonorrhoeae; the possibility of fluoroquinolone-resistant N. gonorrhoeae also should be considered. Hospitalization for initial parenteral therapy is necessary for patients with tubo-ovarian abscess and for those who are pregnant, severely ill, unable to follow a prescribed treatment plan, or unable to tolerate oral antibiotics. Patients also should be hospitalized if a surgical emergency cannot be excluded or if no clinical improvement occurs after three days. Routine screening for asymptomatic chlamydial infection can help prevent PID and its sequelae.