Trichomonas vaginalis was detected by culture or wet-mount examination in 118 (15%) of 779 randomly selected women attending a sexually transmitted disease clinic. Vaginal trichomoniasis was significantly associated with symptoms of yellow discharge, abnormal vaginal odor, and vulvar itching and with signs of colpitis macularis ("strawberry cervix"), purulent vaginal discharge, and vaginal and vulvar erythema. A logistic regression model was used to adjust for coinfections, as well as for demographic, behavioral, and other possible confounding variables. Trichomonas vaginalis remained significantly associated with symptoms of yellow vaginal discharge (odds ratio [OR] = 2.4) and vulvar itching (OR = 3.0) and with signs of colpitis macularis (OR = 241), purulent vaginal discharge (OR = 8.0), vulvar erythema (OR = 2.5), and vaginal erythema (OR = 4.3). The sensitivity of symptoms and signs associated with trichomoniasis was relatively low. Nevertheless, clinical manifestations can be used to identify those patients for whom a wet-mount examination would likely have high yield. Careful clinical examination and selective use of wet-mount examination together with wider use of more sensitive tests for subclinical infection, such as culture or direct immunofluorescent staining of vaginal fluid, could lead to improved detection and control of this infection.