Despite being the cornerstone of behaviour change interventions, a review of the Transtheoretical Model (TTM) highlights that younger populations have been excluded in the development of this model. It is not surprising then that interventions underpinned by the TTM have not been shown to be effective when applied to younger populations. Cognitive development was proposed to account for this age discrepancy. One such construct, adolescent egocentrism comprising of the imaginary audience and the personal fable was explored in relation to both unhealthy behaviour participation and behavioural change. It appeared plausible that the cognitive distortions associated with this construct could affect individuals’ utilisation of those cognitive processes of change proposed by the TTM as being necessary for successful behaviour change. This may provide a fertile avenue for future behaviour change research, extending the interventional scope of the TTM.