Routine testing for Chlamydia trachomatis during gynecological visits, as well as treatment of those found positive, has been suggested as a preventive measure against the serious consequences of chlamydial genital infections, e.g., pelvic inflammatory disease (PID), infertility, and ectopic pregnancy. This article examines the cost and effectiveness of this practice. The study is based on a model that predicts how routine testing and treatment will affect the future number of cases of PID, infertility, and ectopic pregnancy. The costs of test and treatment are estimated, as are the savings resulting from prevention. Results indicate that although routine testing was not effective in reducing the overall morbidity caused by chlamydial infections, for women 18-22 years of age routine testing during regular gynecologic sessions can be a cost-effective personal health service.