Objectives. The purpose of this study was to investigate the theory of planned behaviour's (TPB) mediating hypothesis between the five-factor model of personality and exercise behaviour using an extended TPB model including concepts of affective and instrumental attitude, injunctive and descriptive norm, controllability, and self-efficacy. It was hypothesized that extraversion's activity facet would have a significant direct effect on exercise behaviour while controlling for the TPB, based on the presupposition that activity may represent a disposition that predicts exercise beyond planned behaviour. Design. To test the replicability of these findings, we examined this research question with undergraduate students prospectively and cancer survivors, using a cross-sectional design. Results. Using structural equation modelling, the results indicated that activity had a significant effect (p <.05) on exercise behaviour (study 1 =.20; study 2 =.31) while controlling for the TPB. Conclusions. This study suggests the importance of extraversion's activity facet on exercise behaviour,even when controlling for a TPB model with additional social-cognitive concepts and disparate population samples.