The major aim of the research is to analyse the type and complexity of emotions which adolescent musicians experience before giving a solo music performance. Another aim is to explore the function of these emotions for performance quality. Just before a school concert, students filled out The UWIST Mood Adjective Checklist (UMACL). Right after the performance, both the performing students and competent referees used The Performance Evaluation Scale. The results show that musicians’ pre -performance emotional state is dominated by ambivalent emotions of hope and sadness, as well as joy and anxiety. As a result of a cluster analysis, six clusters were obtained which defined emotional states before the performance: high music performance anxiety, moderate music performance anxiety, calm, mixed emotions, joy with background fatigue, and excitement. The findings show the functional significance of positive emotions and mixed emotions for performance quality.