Chlamydia trachomatis (CT) was detected by culture in 111/600 patients aged 15 to 55; overall prevalence 18.5%, 17% among asymptomatic (52/306) and 20% (59/294) among symptomatic patients. The difference is not significant. Contraceptive practices have no significant influence upon CT prevalence, except for the obvious protective effect of barrier methods. From the history, the clinical and paraclinical findings, four factors (history of genital infection, partner with urogenital symptoms, ectopy, inflammatory changes on a smear) can be combined to produce an index for predicting CT cervical infection. Others factors (age, no pregnancies, mucopus from the cervical os, inflammatory or dysplasic Pap smear, and signs of upper genital tract infection) are indicators of presumption and can be useful to selectively screen asymptomatic or symptomatic patients.