The prevalence of chlamydial infection and associated risk factors were studied in 1531 women from ten clinics in New York State excluding New York City. Overall Chlamydia infection rates were 13.6%; 17.6% in eight high risk family planning and STD clinics, and 5.7% in two low risk college and private clinics. Risk factors for Chlamydia infection included: age < 20 years (odds ratio 1.6), use of oral contraceptives (odds ratio 2.0), a history of having more than one sexual partner (odds ratio 1.7) and, in one clinic where data was available, inflammation on Papanicolaou smears (odds ratio 2.1). These data helped secure funding for Chlamydia preventive services and permitted development of a risk profile (score card) of Chlamydia for each age group. Use of such a score card can be most helpful in assigning which patients could benefit most from Chlamydia cultures, especially in those areas where testing is unavailable or too costly to screen all patients.