Adverse outcomes of teenage sexual activity are common in the United Kingdom. The authors used a computer-assisted interview to ask young adolescents aged 11 to 12 years (N = 6,856) and 12 to 13 years (N = 6,801) who were part of the Avon Longitudinal Study of Parents and Children about romantic and intimate behaviors. A total of 24% of 11- to 12-year-olds, and 41% of 12- to 13-year-olds reported holding hands, and 17% and 32%, respectively, reported having been kissed on the mouth. A minority of 12- to 13-year-olds reported sexual behavior including intercourse. The majority of participants who reported intimate sexual behavior did not regret it. Boys reported all activities more than girls and were less likely to express regret. The findings suggest that the timing and content of sex education should take into account the frequency with which young people are experimenting with sexual behaviors. (Contains 2 tables.)