Men who have sex with men with regard to trans women, people born either biologically male or with ambiguous genitalia who self-identify as female. Some sources consider trans women who have sex with men to be MSM, others consider women who are trans "alongside" MSM, and others are internally inconsistent (defining transgender women to be MSM in one place but referring to "MSM and transgender" in another). Determining the number of men who have ever had sex with another man is difficult. Worldwide, at least 3% of men, and perhaps as high as 16% of men, have had sex at least once with a man. These
Men who have sex with men figures include victims of sexual abuse in addition to men who regularly or voluntarily have sex with men. In the U.S., among men aged 15 to 44, an estimated 6% have engaged in oral or anal sex with another man at some point in their lives, and about 2.9% have had at least one male sexual partner in the previous 12 months. Historically, anal sex has been popularly associated with male homosexuality and MSM. However, many MSM do not engage in anal sex, and may engage in oral sex, frotting or mutual masturbation instead. Among men who have anal sex