The current study investigated the associations among trait perfectionism, worry about mistakes, mistake rumination, L2 anxiety, and willingness to communicate in adolescents. A key element was examining the psychometric properties of a new measure of worry about mistakes as well as the Mistake Rumination Scale and the short Child-Adolescent Perfectionism Scale and its two dimensions (i.e., self-oriented and socially prescribed perfectionism). Our participants were 954 Iranian adolescent English learners. Psychometric tests supported the psychometric properties and use of the mistakes and perfectionism measures. Correlation analyses indicated that both trait perfectionism dimensions were associated with mistake rumination and worry about mistakes, and socially prescribed perfectionism was associated with L2 anxiety. However, self-oriented perfectionism was associated with greater willingness to communicate. Further analyses showed that worry about mistakes and mistake rumination mediated the association that socially prescribed perfectionism had with L2 anxiety. The vulnerabilities of adolescent perfectionists are discussed in terms of the approach-avoidance conflict as it relates to worry about mistakes and pressures to be perfect. It is evident that adolescents who are vulnerable must learn cognitive and emotional regulation techniques to effectively manage mistakes and the pressure to be perfect.