Aversive performance incidents play a role in the development of some anxiety disorders. The role of sensitizing experiences in the development of music performance anxiety (MPA) in adolescent music students has not yet been explored. Two-hundred-and-ninety-eight music students were asked to provide written descriptions of their worst performance, what happened and how they felt, specifying their age at the time, audience members, and any events that occurred subsequent to the performance. Descriptions were scored according to six domains: situational and behavioural factors, affective, cognitive and somatic symptoms of anxiety, and outcome. Scores were summed to provide a linear scale that was compared with self-reported MPA and standardized trait anxiety scores. MPA was best predicted by trait anxiety and gender. The presence of negative cognitions in the worst experience descriptions improved the prediction of MPA over trait anxiety and gender alone. None of the other factors added to the prediction. Females reported more emotional distress than males and had significantly higher total scores. These findings confirm patterns found in adult performers and across other forms of performance anxiety in children (e.g., test anxiety). This study highlights cognitions as an important element to address in the treatment of MPA in young musicians. (Contains 1 figure and 6 tables.)