Extending previous cross-sectional research (e.g., Adie, Duda, & Ntoumanis, 2008), the major purpose of the current study was to test the assumptions of basic needs theory (Ryan & Deci, 2000), hypothesizing a sequence of relationships between coach autonomy support, basic need satisfaction, and indices of well-being over time. The longitudinal mediational role of basic psychological need satisfaction in the association between autonomy support and well-being was also examined. Participants comprised 91 male adolescents from an elite soccer academy. A multisection questionnaire was administered to the participants on six occasions across two competitive seasons. Multilevel regression analyses revealed that perceptions of coach autonomy support positively predicted within-person changes and between-person mean differences in athlete basic need satisfaction and well-being over time. Satisfaction scores for the needs for competence and relatedness were found to correspond to within-person changes in subjective vitality. These same needs partially mediated the coach autonomy support and subjective vitality link over the two seasons. The results are discussed in terms of their theoretical and practical utility.