© 2019 John Wiley & Sons Ltd. All rights reserved. Trichomonas vaginalis is a sexually transmitted protozoan parasite that invades genital epithelia. This highly prevalent pathogen predominately affects women and may play a role in development of upper genital tract complications and cervical cancer, lead to adverse outcomes of pregnancy, and increase risk of HIV acquisition or transmission. Several factors limit our understanding of the epidemiology of trichomonas. The relationship between HIV and discharge-causing sexually transmitted infection (STI) is complex and bidirectional. Genital viral load has been shown to be one of the most important factors in predicting risk of HIV transmission within discordant couples. Though often considered merely a nuisance, trichomonas vaginalis infection in men is known to be an important cause of urethritis, prostatitis, and potentially male factor infertility. The recommended treatment for trichomonas vaginalis infections is a single oral dose of 2-g metronidazole.