Based on theory (Harter, 1978; Sullivan, 1953), the purposes of the present study were to (a) compare context-specific conceptions of friendship quality in youth sport and music, and (b) determine how friendship quality is related to motivational beliefs in sport and music. Adolescents (N = 366; Mage = 12.9, SD = 1.0) who were involved in both organized sport and music completed measures of domain-specific friendship quality, perceived competence, enjoyment, anxiety, and motivational orientation. For purpose one, a repeated-measures MANOVA revealed that (a) boys and girls rated their best sport friends higher in self-esteem enhancement and supportiveness than their best music friends, (b) boys rated their best sport friends higher in loyalty and intimacy, things in common, companionship and pleasant play, and conflict resolution than their best music friends, (c) girls rated positive friendship quality dimensions higher than boys, and (d) there were no domain or gender differences in perceived friendship conflict. For purpose two, structural equation modeling revealed that (a) for sport, positive friendship quality dimensions were directly associated with perceived competence and indirectly associated with enjoyment, anxiety, and motivational orientation, and (b) for music, positive friendship quality and conflict were related to competence motivation variables. Gender moderator analyses revealed slight differences between boys and girls in the pattern of relationships between friendship quality and competence motivation variables in sport and music. Collectively, findings extend the knowledge base by (a) using theoretical frameworks to compare conceptions of friendship quality in two popular extracurricular activities for youth, and (b) demonstrating the significance of friendship quality in motivational beliefs and orientations in sport and music.