Weight-based teasing is common among youth, but little is known about its long-term impact on health outcomes. We aimed to 1) identify whether weight-based teasing in adolescence predicts adverse eating and weight-related outcomes 15 years later; and 2) determine whether teasing source (peers or family) affects these outcomes. Data were collected from Project EAT-IV (Eating and Activity in Teens and Young Adults) (N = 1830), a longitudinal cohort study that followed a diverse sample of adolescents from 1999 (baseline) to 2015 (follow-up). Weight-based teasing at baseline was examined as a predictor of weight status, binge eating, dieting, eating as a coping strategy, unhealthy weight control, and body image at 15-year follow-up. After adjusting for demographic covariates and baseline body mass index (BMI), weight-based teasing in adolescence predicted higher BMI and obesity 15 years later. For women, these longitudinal associations occurred across peer and family-based teasing sources, but for men, only peer-based teasing predicted higher BMI. The same pattern emerged for adverse eating outcomes; weight-based teasing from peers and family during adolescence predicted binge eating, unhealthy weight control, eating to cope, poor body image, and recent dieting in women 15 years later. For men, teasing had fewer longitudinal associations. Taken together, this study shows that weight-based teasing in adolescence predicts obesity and adverse eating behaviors well into adulthood, with differences across gender and teasing source. Findings underscore the importance of addressing weight-based teasing in educational and health initiatives, and including the family environment as a target of anti-bullying intervention, especially for girls.