The frequency of infection following induced first-trimester abortion is 3-5%. Duration of hospitalization is often five days, and the total costs per abortion were 5,400 Dkr (approximately pounds 500) in Denmark in 1979. Sequelae of postabortal infection are similar to and occur with the same frequency as sequelae to "spontaneous" pelvic inflammatory disease. Thus, secondary infertility was found in 10% of women with postabortal infection, spontaneous abortion in 22%, dyspareunia in 20%, and chronic pelvic pain in 14%. The risk of ectopic pregnancy is probably also increased. Surgical scrub cannot sterilize the endocervix and, as a consequence, abortion is performed in a contaminated field. The presence of pathogenic bacteria, i.e. Chlamydia trachomatis, therefore increases the risk of postoperative infection. The organism is found in approximately 7% of those applying for abortion and the risk of sustaining infection is 20%. Other risk factors are previous pelvic inflammatory disease, vaginal infection, first pregnancy and young age. Prophylactic antibiotics halve the incidence of infection, but by applying prophylaxis to risk groups only, the amount of prescriptions can be reduced. Prophylaxis need only be administered peroperatively, and tetracyclines, metronidazol, and penicillin/pivampicillin have been found to be effective. Women applying for abortion should be examined for C. trachomatis and positive cases treated no later than at the time of the abortion.