Acute pelvic inflammatory disease is one of the most important consequences of sexually transmitted infection. Of sexually active women in the United States, one million (or 1 per cent) develop the infection. The sequelae include infertility (10 per cent), ectopic pregnancy (5 per cent), chronic pain (15 per cent), and recurrent infection (25 per cent). Organisms that cause the infection include Neisseria gonorrhoeae, Chlamydia trachomatis, genital mycoplasma, and a wide variety of facultative and anaerobic bacteria. Prompt recognition and therapy are necessary to reduce the sequelae.