A retrospective analysis of 7,879 direct fluorescent antibody (DFA) tests for Chlamydia trachomatis obtained over 24 months from a routine screening program for adolescent women is reported. Tests were positive in 563 women of ages 13 to 24 (mean = 18.1). Monthly positivity rates ranged from 2.59% to 14.02%. Proportions of DFA positive patients were 8.23% (308/3744) and 6.12% (253/4135) during year 1 and year 2, respectively (chi square = 13.2, P = .0003). Of second tests, 12.54% (40/319) were DFA positive. Mean time between first and second tests was 157 days for visit 2 positives, and 90 days for visit 2 negatives (P = .023 by t test). Of visit 2 positive patients, 67.5% (27/40) tested positive greater than 30 days after the initial test; 72.5% (29/40) were positive within 180 days. Ninety-two per cent (23/25) of visit 2 positive patients were negative at visit 3. The initial annual prevalence of 8.23% was consistent with previous studies from this clinic. The decline in proportion of C. trachomatis positive women (while gonorrhea rates were stable) suggests an influence of aggressive case finding. That most women test DFA negative within a time period often used for tests of cure for sexually transmitted diseases (i.e., within 30 days) and that many women who test negatively test positive within a short time suggest that women with chlamydial infection be rescreened at longer intervals, perhaps every 6 months.