From Encyclopedia of Sex and Sexuality
Human sexual behavior has traditionally been divided into two categories—heterosexuality and homosexuality. Individuals who identify themselves as heterosexual are assumed to have sexual relationships only with persons of the opposite sex; persons who identify themselves as homosexual are assumed to have sexual relationships only with persons of the same sex. These patterns are frequently believed to be fixed during childhood and to remain constant throughout a person’s lifetime.
Although research into bisexual behavior has lagged behind that of heterosexual and homosexual behavior, we now know that the sexual lives of many individuals do not fall easily into either of these categories. Many individuals will be sexually attracted to, or have sexual relationships with, both men and women at some time during their lives. We also know that there are many different patterns of bisexual behavior and that people engage in such behavior for a variety of reasons.
To date, researchers have not identified specific biological, psychological, or sociological determinants of sexual attraction. The deteminants, as well as the development of bisexual behavior, may differ from person to person.
 The Definition of Bisexuality
The term bisexual may be used to describe an individual’s sexual behavior or sexual identity. Bisexual behavior usually refers to sexual contact with both men and women. The timing of these sexual contacts may vary considerably, depending on the individual. Some persons have sexual relationships with men and women at the same time, while others alternate with male and female partners, one after the other. Some individuals engage in bisexual behavior for relatively short periods of their lives, while for others it is a more stable behavior pattern, beginning in adolescence and lasting throughout adulthood.
While persons who engage in bisexual behavior may describe themselves as bisexual, many identify themselves as heterosexual or homosexual. The limited research we have suggests this may be particularly true of African-American and Latino bisexual men and African-American women.
 Prevalence and Patterns of Bisexuality
There is relatively little information available on the prevalence of either male or female bisexual behavior in the United States. Estimates from national samples of sexual behavior during 1970–1990, reported in the Journal of Sex Research in 1991, suggest that approximately 20 percent of men report some sexual contact with men during their lifetime and approximately 6 to 7 percent during adulthood. Male sex relationships with males during adulthood tend to be episodic or sporadic and most of these men also have sexual relationships with women. Comparable data on bisexual behavior in women have not been published; however, it has been estimated that approximately one-third as many women as men have ever had a sexual relationship with both men and women.
Several studies have suggested that there may be cultural differences in bisexual behavior, and that African-American and Latino men are more likely than white men to have sex with both men and women. African-American and Latino bisexual men are more likely than white bisexual men to identify themselves as heterosexual, to be married, and to not tell their female partners about their same-sex contacts. African-American lesbian and bisexual women report more extensive heterosexual experiences than do white lesbian or bisexual women. The reasons for these cultural patterns are unclear.
Many different patterns of bisexual behavior have been identified among men. Examples include youths exploring their sexuality, men who have sex with other men for money or drugs, men in prisons or other all-male institutional settings, men in primary relationships with women, and men who identify themselves as bisexual. Most men engaging in bisexual behavior do not even fall into one of these identifiable groups; men who identify themselves as bisexual may represent the smallest of all groups. However, these patterns suggest that not all bisexuality may be described as a transitional period in an individual’s life, or a form of denial of one’s homosexuality. Indeed, most persons who engage in bisexual behavior may do so because they are sexually attracted to both men and women during a prolonged period in their lifetimes.
Very little is understood about patterns of bisexual behavior in women. Like men, they are believed to have very diverse life-styles and sexual histories. The development of a bisexual life-style may be somewhat different between men and women. However, bisexual women report having, on average, earlier opposite-sex sexual experiences but later same-sex attraction and sexual experiences. Unlike male bisexuals, who may marry women despite an awareness of same-sex attraction, female bisexuals’ awareness of sexual attraction to other women typically occurs after marriage. Bisexual experimentation may begin with intense, affectionate friendships among women.
 Sexual Behaviors
The range of sexual behaviors reported by bisexual men and women mirrors those of their homosexual and heterosexual counterparts. Estimates of the frequency of specific sexual practices with male and female partners are available primarily from recent AIDS-related research, which targets high-risk populations and focuses on specific AIDS-related behaviors. Thus, they are probably not representative of the larger population of bisexual men and women. However, such studies suggest that bisexual men may engage in more sexual risk behaviors than exclusively heterosexual men, but fewer than exclusively homosexual men. In general, studies have shown that bisexual men report greater numbers of sex partners and engage in more oral and anal intercourse than heterosexual men, but less than homosexual men. While married bisexual men report high numbers of sex partners, they report engaging in anal intercourse less frequently. Bisexual men who identify themselves as gay may engage in less frequent sexual risk behaviors, perhaps because of exposure to HIV educational programs in gay communities. Only a small minority (perhaps 20 percent ) of bisexual men in primary relationships tell their wives or other female partners about their same-sex sexual contacts.
To date, very few studies have examined the sexual practices of bisexual women. In a recent AIDS-related study, 88 percent of women who had engaged in sex with a man since 1980 but currently identified themselves as lesbians reported engaging in vaginal or anal intercourse with men without condoms. Nearly 32 percent of these women reported having a sexual relationship with a bisexual man. Indeed, these bisexual women were more likely to engage in sexual risk behaviors, such as anal intercourse, with a bisexual male partner than were bisexual women having sexual intercourse with exclusively heterosexual men. The frequency of bisexual women having a sexual relationship with bisexual men is unclear, but such contact may increase the woman’s risk for HIV.
It is important to note that most gay men and lesbian women have engaged in sex at least once with a person of the opposite sex. In fact, between 15 and 26 percent of gay men and 20 and 35 percent of lesbian women have been married.
 Health Risks of Bisexuality
Concern with HIV transmission has prompted an examination of the rates of sexually transmitted diseases (STDs), including aids, among bisexual men and women. In general, bisexual men report lower rates of STDs than exclusively homosexual men and higher rates than exclusively heterosexual men. Of the 65,389 men who have had sex with men and whose AIDS diagnosis was reported to the United States Centers for Disease Control and Prevention through June 1990, 74 percent reported having sex only with men and 26 percent with both men and women since 1977. Given the large number of infected gay men in the United States and the greater ease of HIV infection from man to man than from woman to man, it is probable that most bisexual men were infected through same-sex sexual contact.
Data on STDs among bisexual women are strikingly different from those for bisexual men. Bisexual women are more likely than lesbian women to report abnormal Pap smears, cystitis, genital herpes, gonorrhea, and vaginal infections. Through 1989, 103 cases of AIDS in bisexual women had been reported, compared to 79 cases in lesbian women. Nearly all (79 percent) of these women reported injection drug use as their primary risk factor for HIV; the remainder reported sex with a male partner at risk for, or infected with, HIV (16 percent), or a history of blood transfusion (4 percent). While there is potential for transmission of HIV and other diseases through woman to woman sexual contact, the risk for bisexual women is related primarily to the frequency of intercourse with a male partner. Additional studies have reported that bisexual men are more likely to have injected drugs and to have received money or drugs in exchange for sex. However, because of the sampling procedures used for these studies, the ability to make generalizations based on these data with regard to the larger population of bisexual men is unknown.
Bisexuality has not been systematically studied in the United States and knowledge of bisexuals’ behavior is tentative at best. Given the numbers of persons who are bisexual or whose lives are touched by those who are, it is important that we develop greater sensitivity and scientific understanding of how individuals manage life-styles that include sexual relationships with both men and women.