Mycoplasma hominis colonizes the vagina of women and the urethra of men. The organism is also isolated from beneath the foreskin of uncircumcised men. It is sexually transmitted. M. hominis is isolated from a small proportion of children and sexually inexperienced adults. Among sexually experienced adults, rates of colonization rise in relation to the lifetime number of sexual partners. Even with sexual experience taken into account, the organism is more prevalent among young individuals and among blacks. The use of barrier methods of contraception (condom and diaphragm) reduces the likelihood of colonization with M. hominis.