Objective To examine longitudinal trends from 1999-2010 in weight-related teasing as adolescents transition to young adulthood and to examine secular trends in teasing among early and middle adolescents over the same time period. Design and Methods To examine longitudinal changes we used data from 2,287 participants in Project EAT-III, an ongoing cohort that followed two age cohorts of adolescents from 1999 to 2010. Over the study period the younger cohort transitioned from early adolescence to early young adulthood and the older cohort transitioned from middle adolescence to middle young adulthood. To examine how levels of teasing among early and middle adolescents changed from 1999-2010 (secular trends), we compared baseline data from EAT-I to cross-sectional data from a new cohort of early and middle adolescents that was established in 2010. Results In 1999, 29% of early adolescent and 23% of middle adolescent females reported being teased. Approximately 18% of males in both age groups reported being teased in 1999. Longitudinal trends suggest that weight-related teasing remained stable among all subgroups as they transitioned to young adulthood, except among early adolescent males where teasing increased to 27% in early young adulthood. Analyses of age-matched secular trends show that teasing decreased by 10.4% among early adolescent females and by 7.6% among middle adolescent males from 1999-2010. Conclusion Results suggest that interventions that focus on reducing weight-based discrimination are needed throughout adolescence and young adulthood. The secular decrease in weight-related teasing is promising, but the high prevalence of teasing remains a public health concern.