Endocervical Chlamydia trachomatis infection was found in 13 of 162 volunteer female university students (8%). Infection was correlated with younger age (p less than 0.05), less than or equal to 4 years of intercourse (p less than 0.05), a history of gonorrhea (p less than 0.01), and exposure to a partner with urethritis (p less than 0.01). Women who used intrauterine or barrier contraception had less infection (2%) than did women who used oral contraception (14.3%, p less than 0.05) or none at all (10.7%, p less than 0.05). Infection was strongly associated with a cervicitis score calculated from erythema, ectopy, discharge, and secretions that contained white blood cells (p less than 0.0001). By multivariate analysis, a proposed clinical approach was arrived at for testing for chlamydial organisms all women with cervicitis who were not using barrier contraception. The positive predictive value of this approach for chlamydial infection was 28%, and the negative predictive value 98.4%. Cervical ectopy was increased in women who used oral contraception (p less than 0.01), and infection was increased in women with ectopy, regardless of their contraceptive method (p less than 0.001). These results will aid in more rapid diagnosis of endocervical chlamydial infection and in the choice of contraception in young women and high-prevalence groups.