Objectives: To explore the hypothesised reciprocal relationship between fundamentalmovement skill (FMS) competence and physical activity (PA) behaviour and investigate the role of health-related fitness (HRF) as a mediator of this association. Design: Cross-sectional. Methods: Adolescents aged 12.80 years (SD±.45 years) were recruited from 20 schools (n = 222, 50% male). FMS (TGMD, TGMD-2, Victorian Skills Manual), moderate-to-vigorous physical activity (MVPA) per day (Actigraph accelerometers for a 7-day period), and HRF (3 minute Queens College step test used to calculate a predicted VO2max value) were assessed. Descriptive statistics and frequencies were calculated. Preacher and Hayes (2004), bootstrap method was used to assess the hypothesised reciprocal relationship between FMS and PA and the potential mediating effect of VO2max on the reciprocal relationship between PA and FMS. Mediation was determined using the logic of Baron and Kenny (1986). Results: A reciprocal relationship was found between PA and FMS (τ' = 0.22, p<0.01 in both directions). VO2max mediated 17% and 19% of these relationships, respectively. Conclusion:Analyses suggest a reciprocal relationship between PA and FMS exists in youth. VO2max explained part of this relationship, in both directions, suggesting that increasing adolescent fitness will serve to enhance both PA participation and skill development. The unexplained variance in the reciprocal relationship between PA and FMS must be explored further in an attempt to understand and target this relationship, better.