Over the past decade, the percentage of high school students who say they are virgins has risen significantly, according to a report published Friday by the federal Centers for Disease Control and Prevention.
Last year, the report found, high school virgins outnumbered those who had engaged in sexual intercourse, 54 percent to 46 percent. A decade earlier, the percentages were the opposite.
The study, based on self-reported data from more than 10,000 high school students, also found other evidence of more conservative sexual behavior.
Among sexually active students, 57.9 percent said they had used condoms when they last had intercourse, up from 46.2 percent a decade earlier.
There was also a decline in the percentage of high school students who had had four or more sex partners, with 14.2 percent reporting such experience in 2001, compared with 18.7 percent in 1991.
"We have less kids at risk than we used to have, given this combination of factors all working together - fewer kids having sex, fewer having multiple partners and more using condoms," said Laura Kann, one of the authors of the report.
"It's still too many," Kann said, but added that the trends "are all consistently heading in the right direction."
Most experts say the decline in sexual intercourse can be attributed to a combination of factors, including abstinence programs, fear of AIDS, and an increase in oral sex, which many teen-agers regard as less dangerous and less intimate than intercourse.
"The increase in contraceptive use is the strongest trend we're seeing," said David Landry, a senior research associate at the Alan Guttmacher Institute.
While there is always some doubt about the accuracy of self-reports on sexual activity, experts in the field say the findings are bolstered by the fact that adolescent pregnancy and birth rates have also declined.
A separate study on adolescent sexual behavior, released last week by Child Trends, a nonprofit research group in Washington, challenged the popular belief that most teen-agers lose their virginity in the after-school hours, in the back seat of a car, in a motel or in a park.
In fact, the Child Trends study reported, 70 percent of sexually experienced teen-agers first had intercourse after 6 p.m., and most often in their family's home or that of their partner.