The prevalence of Chlamydia trachomatis infection of the cervix uteri and its possible association with postabortal pelvic inflammatory disease (PID) were investigated in women subjected to first-trimester-induced abortion. None of the women had signs or symptoms of genital infection at the time of abortion. Chlamydia organisms were isolated from the cervix/urethra in 33 (10%) of 333 women. Women with a positive Chlamydia culture were comparable to women with a negative culture in regard to gestational age at the time of abortion. However, Chlamydia-positive women were significantly younger and had gonorrhea more often than Chlamydia-negative women. Two hundred seventy (81%) of the women were followed up 1 month after the abortion. Thirty-two of these developed postabortal PID. Eight (28%) of 29 women with a positive Chlamydia culture and 24 (10%) of 241 women with a negative culture developed postabortal PID. This difference is significant (P less than .025) and indicates that the presence of Chlamydia in the cervical canal at the time of abortion in asymptomatic women increases the risk of postabortal PID.