This document provides information about Trichomonas vaginalis, a protozoan parasite that causes the sexually transmitted infection trichomoniasis. It describes the characteristics of T. vaginalis trophozoites, symptoms of infection, methods of diagnosis, and transmission routes. Trichomoniasis is common worldwide and symptoms in women can include vaginal discharge and irritation while men may experience mild urethritis. Diagnosis involves microscopic identification of trophozoites in vaginal or urethral discharge or urine samples.