PURPOSE: North American research finds increased sexual risk-taking among teenagers with same-sex partners, but understanding of underlying processes is limited. The research carried out in the United Kingdom compares teenagers' early sexual experiences according to same- or opposite-sex partner, focusing on unwanted sex in addition to risk-taking, and exploring underlying psychosocial differences. METHODS: Multivariate analyses combined self-reported data from two randomized control trials of school sex education programs (N = 10,250). Outcomes from sexually experienced teenagers (N = 3,766) were partner pressure to have first sex and subsequent regret, and sexual risk measures including pregnancy. Covariates included self-esteem, future expectations, substance use, and communication with mother. RESULTS: By the time of follow-up (mean age, 16), same-sex genital contact (touching or oral or anal) was reported by 2.3% of teenagers, with the majority also reporting heterosexual intercourse. A total of 39% reported heterosexual intercourse and no same-sex genital contact. Boys were more likely to report partner pressure (Odds ratio [OR] = 2.56, 95% confidence intervals [CI] = 1.29-5.08) and regret (OR = 2.32; 95% CI = 1.39-3.86) in relation to first same-sex genital contact than first heterosexual intercourse, but girls showed no differences according to partner type. Teenagers with bisexual behavior reported greater pregnancy or partner pregnancy risk than teenagers with exclusively opposite-sex partners (girls, OR = 4.51, 95% CI = 2.35-8.64; boys, OR = 4.43, 95% CI = 2.41-8.14), partially reduced by attitudinal and behavioral differences. CONCLUSIONS: This UK study confirms greater reporting of sexual risk-taking among teenagers with same-sex partners, and suggests that boys in this group are vulnerable to unwanted sex. It suggests limitations to the interpretation of differences, in terms of psychosocial risk factors common to all adolescents.