Over the past decade, considerable legal and policy discussion has emerged about sexual activity between young teens and older individuals. This discussion has been prompted by the growing awareness of the personal and societal costs of this activity. Sex between young teens and older individuals is linked with risky sexual behaviors that could lead to unintended pregnancy and childbearing, as well as to sexually transmitted infections. Among sexually experienced teens, having sex with someone who is older has been associated with reduced and inconsistent use of contraception, including reduced use of condoms, and a greater risk of a teen pregnancy. More than one in four babies born to mothers between the ages of 15 and 17 were fathered by someone who was five or more years older. On average, young teens who have sex with an older individual report a larger number of sexual partners during the high school years and higher levels of drug and alcohol use than do other sexually experienced teens. (Contains 8 figures and 18 endnotes.)