We prospectively determined the prevalence of Chlamydia trachomatis infection in patients presenting to an emergency department over a 4-month period who received pelvic exams. We compared the percentage of cases of Chlamydia diagnosed by the Chlamydiazyme immunoassay with the percentage diagnosed clinically by emergency physicians. Over the study period, 326 pelvic exams were performed. Of 36 patients (11%) with positive tests, 16(44%) were treated clinically for pelvic inflammatory disease. Twenty (56%) received neither appropriate antibiotic treatment nor a gynecology referral based on clinical exam alone. We statistically evaluated the data using the hypothesis test for two proportions from one group. The difference was significant (Z = 4.6, p < 0.001).