ABSTRACT. Objectives. Little is known about the practice patterns of primary care providers as they relate to assessing risk of and screening for chlamydial infections, an important cause of preventable reproductive morbidity in young women in the United States. The present cross-sectional study was undertaken to assess levels of chlamydia testing, sexual history taking, and prevention practices by Colorado primary care physicians, nurse practitioners, and physician assistants who provide gynecologic care to adolescent females (13-19 years old).Methods. Between July 1998 and October 1998, an anonymous, self-administered questionnaire was mailed to a 25% random sample (n ؍ 1265) of Colorado physicians (family practitioners, internal medicine specialists, obstetrician-gynecologists, and pediatricians), nurse practitioners, and physician assistants. Practitioners were identified through professional organization membership, state-licensing bodies, and listings in the yellow pages.Results. After estimating the eligibility rate among nonrespondents, the adjusted response rate was 71.5%. Only 53.8% of providers reported regularly testing sexually active female adolescents for chlamydia; 71.8% of providers regularly took a sexual history. Female providers reported significantly higher levels of regularly taking a sexual history (87.2% vs 60.6% of males), feeling comfortable discussing sex (94.4% vs 77.8%), discussing sexually transmitted disease (STD) prevention (81.5% vs 71.3%), and testing for chlamydia (64.4% vs 38.6%). Among provider types, obstetrician-gynecologists, nurse practitioners, and pediatricians were most likely to report regularly taking a sexual history (90.1%, 88.6%, and 76.0%, respectively). Internal medicine specialists were the least likely to report taking a sexual history (43.9%). Pediatricians and nurse practitioners were the most likely to report testing sexually active adolescent females for chlamydia (74.1% and 70.1%, respectively), whereas physician assistants and internal medicine specialists were the least likely (46.0% and 38.5%, respectively).In multivariate analysis, variables independently associated with regularly taking a sexual history included female provider gender (odds ratio [OR]: 5.5; 95% confidence interval [CI]: 2.9 -10.9), obstetrics/gynecology specialty (OR: 4.0; 95% CI: 1.7-10.3; referent group: family practitioners), and provider comfort level in discussing sex (OR: 4.9; 95% CI: 2.3-11