INTRODUCTION Trichomonas vaginalis is considered the most prevalent curable sexually transmitted infection, and its occurrence exceeds that of gonococcal and chlamydia infections. This parasite has been identified as responsible for the increased risk of transmission of HIV and has also been associated with prostate and cervical cancer. Many carriers of T. vaginalis are asymptomatic and, when experiencing a health problem, they most often have nonspecific symptoms. The aim of this research was to estimate the presence of T. vaginalis and the associated factors in women of childbearing age at a primary health care clinic in the Federal District of Brazil. METHODOLOGY A cross-sectional study was conducted with consecutive sampling of an outpatient population of women of childbearing age (excluding minors and pregnant women). The women answered a questionnaire and were examined. After vaginal pH measurement and whiff testing, a vaginal secretion sample was obtained for inoculation in TYM, a specific T. vaginalis culture medium. RESULTS The presence of T. vaginalis was identified in 16% of the sample. Fewer lifetime sexual partners and consistent condom use were identified as factors of protection against the infection. Complaints of dyspareunia were proportionally higher among women with positive cultures for T. vaginalis. CONCLUSIONS The prevalence of T. vaginalis infection was high in the sample studied. The infection was positively associated with the number of lifetime sexual partners, and consistent condom use was a protective factor. Vaginal complaints were more common among women with T. vaginalis, but only dyspareunia had significant association.