Some more highlights from the study:
Ninety-seven percent of men and 98 percent of women aged 25 to 44 have had vaginal intercourse.
Ninety percent of men and 88 percent of women reported having had oral sex with an opposite-sex partner.
Forty percent of men and 35 percent of women have had anal sex with an opposite-sex partner.
Men aged 30 to 44 reported an average of six to eight female sexual partners so far while women reported about four. This is similar to studies conducted in the early 1990s.
About 6.5 percent of men aged 25 to 44 have had oral or anal sex with another man. Three percent of males 15 to 44 years have had oral or anal sex with another male in the last 12 months (1.8 million people).
Eleven percent of women aged 25 to 44 reported having had a sexual experience with another woman. Four percent of females reporting having a sexual experience with another female in the last 12 months.
Six percent of males and 11 percent of females had had same-sex contact in their lifetimes. While this percentage remains relatively unchanged for men since the early 1990s, the proportion of women has soared unexpectedly from 4 or 5 percent to 14 percent among women aged 18 to 29. "We may want to consider the possibility that women are trying to reduce their risk of STDs," Mosher said.
Ninety percent of men aged 18 to 44 thought of themselves as heterosexual, 2.3 percent as homosexual. 1.8 percent bisexual and 3.9 percent "something else" while the rest did not answer the question. The numbers were almost exactly the same for women.
Twenty-nine percent of men who had ever had sexual contact with another man were tested for HIV in the past year compared with 14 percent of men with no same-sex contact.
Seventeen percent of men who had ever had sexual contact with another male had been treated for a non-HIV STD, compared with 7 percent of those who had never had male-on-male sexual contact.
Among men 15 to 44 who had at least one sexual partner in the last 12 months, 39 percent used a condom at their most recent encounter. The figure was 65 percent among never-married males and 24 percent among married males.
Ninety-one percent of males who had ever had sexual contact with another male used a condom the last time they had sex, compared with 36 percent of men who never had sex with another male.