The goal of this study was to explore the longitudinal associations between youth activity participation and adjustment over the high school years by examining (a) correlations between participation and adjustment growth curves, and (b) bidirectional links between participation and adjustment from one year to the next. Participation was operationalized as the total number of hours spent in sports, performance and fine arts, and youth clubs over a school year. Indicators of adjustment included school grades, alcohol use, and depressive symptoms. Youth (n = 362; mean age = 13.38, SD = 0.42; 59% girls) were surveyed annually from grades 7 to 10 using questionnaires and phone interviews. Growth curve results revealed that: (a) sports were positively associated with alcohol use; (b) performance and fine arts were negatively linked to depressive symptoms, and (c) youth clubs were positively associated with school grades, and negatively linked to alcohol use and depressive symptoms. The bidirectional analyses revealed few significant links from one year to the next, with the exception of performance and fine arts and grades. (Contains 2 tables and 2 figures.)