The overall prevalence of Chlamydia trachomatis among 873 abortion-seeking women was 9.3% during 1985. Significantly higher age-specific prevalences of C. trachomatis occurred among younger women (p less than 0.001). None of 17 women treated for C. trachomatis before the abortion was carried out, was readmitted to the hospital. Of 64 Chlamydia-positive women, who commenced treatment within the first 2 weeks after the abortion was carried out, 14.1% were readmitted to the hospital, compared with 5.7% of Chlamydia-negative women (p less than 0.02). Postabortal salpingitis was verified at readmission among 10.9% of Chlamydia-positive women and 3.2% of Chlamydia-negative women (p less than 0.01). An analysis of screening of all abortion-seeking women is estimated to be worthwhile when the prevalence of C. trachomatis exceeds 4.3%. We recommend screening for Chlamydia trachomatis of all abortion-seeking women, 30 years or younger, at the pre-abortion visit, provided that treatment can be completed before the abortion is carried out.