This study is part of the 2006 edition of the Health Behaviour in School-Aged Children (HBSC) study. The data presented was drawn from a sample of 21,811 Spanish adolescents ranging from 11 to 18 years of age. Through a cluster analysis, General Lineal Model, significance and effect size tests, we obtained relevant information about the physical activity habits and sedentary behaviours of Spanish adolescents. It is evident that there is a risk situation in older adolescents, especially girls. These results have the advantage of relating to a global health score; clear indicators of the advantages of an active lifestyle for adolescents were obtained. Furthermore, these data provide information that is relevant to the displacement hypothesis, which is widely discussed in the scientific literature. In short, this paper provides interesting keys for theoretical debate and practical action in the field of physical activity during adolescence.