Weight-based disparities in mental health impair the well-being of youth with overweight and obesity, who comprise a growing majority of young people in the United States. This review summarizes research regarding the extent of weight-based disparities in youth mental health and describes the social underpinnings of these disparities across contexts. Youth with high weight face frequent stigmatization (e.g., bullying, victimization, negative judgment), particularly in the school setting. Weight-based disparities in youth mental health emerge not because of high body weight itself, but because of the stigma associated with having high body weight. As such, policy actions need to address weight stigma. Empirical evidence can inform sound policies to reduce the stigma experienced by youth with high weight in order to support equitable mental health outcomes for youth with diverse body sizes.