Background: Trichomonas vaginalis is the most prevalent nonviral sexually transmitted infection in the United States, affecting 3.1% of women of reproductive age. Infection is associated with HIV acquisition and pelvic inflammatory disease. In the United States, Centers for Disease Control and Prevention guidelines recommend testing all women with vaginal discharge for T. vaginalis, but except for HIV-infected women, there are no national guidelines for screening asymptomatic persons. The objective of this analysis is to assess testing and screening practices for T. vaginalis among symptomatic and asymptomatic women in the sexually transmitted disease (STD) clinic setting. Methods: We analyzed data on demographics, clinical presentation, and laboratory testing for all women visiting a clinician in 2010 to 2011 at any of 15 STD clinics participating in the STD Surveillance Network. Prevalence of laboratory-confirmed T. vaginalis infection was calculated among symptomatic women tested and among asymptomatic women screened. Results: A total of 59,176 women visited STD clinicians: 39,979 were considered symptomatic and 19,197 were considered asymptomatic for T. vaginalis infection, whereas 211 were HIV-infected. Diagnostic practices varied by jurisdiction: 4.0% to 96.1% of women were tested or screened for T. vaginalis using any laboratory test. Among 17,952 symptomatic women tested, prevalence was 26.2%. Among 3909 asymptomatic women screened, prevalence was 6.5%. Among 92 HIV-infected women tested/screened, prevalence was 29.3%. Conclusions: Trichomoniasis is common among STD clinic patients. In this analysis, most STD clinics tested symptomatic women seeking care, in accordance with national guidelines. All HIV-infected women should be screened annually. Additional evidence and national guidance are needed regarding potential benefits of T. vaginalis screening in other asymptomatic women. Copyright © 2013 American Sexually Transmitted Diseases Association.