general population surveys indicate even higher differences in proportions of men and women engaging in casual or commercial sex. These gender differences in sexual behaviors in Asia and Latin America also exceed gender differences in the industrialized countries (26, 27).
Despite recent interference from Congress, several methodologically sound surveys of sexual behavior have been conducted in the United States. Zelnik and Kantner (29) studied adolescent sexual behavior in national probability samples in 1971, 1976, and 1979, documenting steadily increasing rates of premarital intercourse by teenaged females throughout the 1970s. The National Survey of Adolescent Males (30, 31) found that from 1988 to 1991, 17.5- to 19.0-year-old males experienced a significantly younger mean age of first intercourse and a significant increase, from 2.0 to 2.6, in the mean number of sexual partners over the past 12 months, with no increase in frequency of condom use. The 1973, 1976, 1982, and 1989 cycles of the National Survey on Family Growth (32) showed a continuing increase in the proportion of female teenagers 15–19 years old who were sexually experienced, from 28.6% in 1970 to 51.5% in 1988, including an increase among white teenagers from 44.1% to 51.5% during the AIDS era from 1985 to 1988. Similarly, the General Social Survey collected limited data annually from 1988 to 1990 on sexual behaviors of U.S. adults (33), providing perhaps the best comparison yet available of recent sexual behaviors of males and females, with data stratified by age, race, and marital status. Results help explain age and race disparities in rates of bacterial STD in the United States and suggest that >22.5 million U.S. adults had 2 or more sex partners during the preceding year, with an estimated 4.8 million having had 5 or more partners. The 1990 National AIDS Behavioral Surveys (34) assess HIV-related sexual risk behaviors. Most recently, from the landmark 1990 National Survey of Men (NSM-I), a series of five articles by Tanfer and coworkers (70–74), concerning sexual behaviors of men 20–39 years old, appeared in Family Planning Perspectives, March/April 1993. Age and race/ethnicity differences in numbers of sexual partners paralleled age and race/ethnicity disparities in bacterial STD rates in the United States and the General Social Survey results (33). We await results of the national survey of female sexual behavior from the same group.
These trends in heterosexual behavior over the last decade contrast with the well-documented dramatic decline in unsafe sexual behavior among homosexual/bisexual men, which strikingly cut rates of early