Much of the research on sexual orientation disparities in eating disorder behaviors has been conducted in the USA, Canada, and Australia. Data on the associations of sexual orientation and eating disorder symptoms among adolescents in the UK are lacking. Participants were children from the Avon Longitudinal Study of Parents and Children, a youth cohort born 1991-1992 (n = 5048; 53% female; 12% sexual minority). Sexual orientation was assessed at 16 years. Eating disorder symptoms were assessed at 14 and 16 years. Multivariable regression models (adjusting for BMI, ethnicity, socioeconomic status) examined associations between sexual orientation and (1) odds of past-year purging and binge eating, and (2) mean differences in body dissatisfaction, pressure to increase muscularity (boys only), and Dutch Eating Behavior Questionnaire subscales. At age 14, gay and bisexual boys and mostly heterosexual girls reported greater body dissatisfaction than their same-gender heterosexual peers. All sexual minority boys and mostly heterosexual girls reported greater mean dysfunctional eating behaviors than their same-gender heterosexual peers. At age 16, gay and bisexual boys had 12.5 times the odds of heterosexual boys of binge eating; mostly heterosexual boys had over three times the odds of reporting binge eating. Sexual minority girls had over twice the odds of heterosexual girls of purging and binge eating. By mid-adolescence, sexual minority youth in the UK had elevated risk for eating disorder symptoms, suggesting the need for early prevention efforts.