The study longitudinally tracked the relationship among challenge/skill balance, flow, and performance anxiety in 27 student musicians over the course of a semester as they worked toward a recital of a piece of music. Using hierarchical linear modeling, the balance between the challenge of a passage of music and the perceived skills necessary to play that music was found to be significantly and consistently correlated with optimal experience. Results of moderated multiple regression indicated that skill level moderated the relationship between challenge, flow, and performance anxiety. Results also indicated that flow and performance anxiety were antithetical experiences, such that when flow was highest, performance anxiety was lowest and vice versa. These findings are discussed in terms of the application of flow theory to understanding performance, and the practical implications for reducing task-specific anxiety.