Adolescence is a pivotal period in lifelong health trajectories, in part by seeding and consolidating individual differences in behaviours and experiences that have direct and indirect effects on health. Pubertal development may also shape health, via changes in health behaviours, as well as via metabolic and neuroendocrine processes. The effects of puberty may also vary according to whether a person begins puberty earlier or later than same-age, same-sex peers. These psychosocial and psychobiological developmental processes can influence health, resulting in changes that are measurable via cardiometabolic as well as neuroendocrine assessments, including an assessment known as allostatic load. Allostatic load measures the disruption to healthy function as a result of high levels of stress, but are also determined by health behaviours. Pubertal timing and adolescent psychosocial development are associated with health behaviours, and so these psychosocial and biological changes may in turn influence allostatic load. This study will examine if pubertal timing and allostatic load are related, and if so, examine the influence of stress and health behaviour on the strength of the association. Using secondary data from a longitudinal study of the wellbeing of ∼9000 children and adolescents, a mediation model will be used to test the association of pubertal timing in early adolescence and allostatic load in late adolescence, and then test if any effect is via the experience of psychosocial stress or health behaviours. The findings will contribute to the knowledge of the associations of adolescent psycho-biosocial development, health behaviour, stress and adolescent health.