Adhesion and penetration of Gardnerella vaginalis into the male urethral and female vaginal epithelial cells were evaluated in a prospective cohort study of infected females and their sexual partners. Vaginal secretions of 10 women with culture proven G. vaginalis infection and semen samples of their asymptomatic husbands were analyzed with conventional optical and electron microscopy. G. vaginalis was isolated in 50% of the male sexual partners of women harboring the microorganism. G. vaginalis adheres to the plasmatic membrane and penetrates into the cytoplasm of both vaginal and urethral epithelial cells. The ability of G. vaginalis to colonize the male lower genital tract may have clinical relevance with respect to the role of the male partner in the reinfection of women.