Weight-based victimization has become increasingly reported among overweight youth, but little is known about adolescents' perceptions and observations of weight-based teasing and bullying. This study examined adolescents' observations of and reactions to weight-based victimization toward overweight students at school. Adolescents (N = 1555) at 2 high schools in central Connecticut completed a questionnaire that examined their perceptions of how common weight-based victimization is compared to other forms of teasing at school, what types of weight-based teasing are frequently observed, who typical perpetrators of weight-based victimization are, and their own reactions to observed teasing incidents. Participants also completed the Fat Phobia Scale. Participants perceived being overweight as a primary reason that peers are victimized at school. At least 84% of participants observed overweight students being teased in a mean way and teased during physical activities, and 65% to 77% of students observed overweight and obese peers being ignored, avoided, excluded from social activities, having negative rumors spread about them, and being teased in the cafeteria. Most students also observed verbal threats and physical harassment toward overweight and obese students. Although the majority of participants felt comfortable stepping in to help an overweight peer who has been teased, many remain passive bystanders following these incidents. Youth perceive frequent and multiple forms of weight-based victimization. Schools' efforts to address weight bias and assist overweight and obese students are important. © 2011, American School Health Association.