This study examined the impact of the middle school transition on general anxiety trajectories from middle childhood to middle adolescence, as well as how youths' individual vulnerability and exposure to contextual stressors were associated with anxiety trajectories. Participants were 631 youth (47% boys, M age = 7.96 years at Time 1), followed for 7 successive years from second to eighth grade. Teachers reported on youths' individual vulnerability to anxiety (anxious solitude) in second grade; youth reported on their anxiety in second to eighth grade and aspects of their social contexts particularly relevant to the school transition (school hassles, peer victimization, parent-child relationship quality, and friendship quality) in sixth to eighth grade. The results revealed two subgroups that showed either strongly increasing (5%) or decreasing (14%) levels of anxiety across the transition and two subgroups with fairly stable levels of either high (11%) or low (70%) anxiety over time. Youth in the latter two subgroups could be distinguished based on their individual vulnerability to anxiety, whereas youth with increasing anxiety reported more contextual stressors and less contextual support than youth with decreasing anxiety. In sum, findings suggest that the middle school transition has the potential to alter developmental trajectories of anxiety for some youth, for better or for worse.