The benefits of exercise are well documented, nevertheless, physical activity decreases progressively with age, a trend exacerbated in those who have fallen. An important predictor of exercise behaviour is the extent to which motivation for exercise has been internalised into one's identity, however, we know little about changing health behaviours in older people, with calls for longitudinal studies to aid understanding. Grounded in self-determination theory, the present study explored the role of self-talk in the process of identity change during the initial ten weeks of an exercise referral falls prevention programme. Six participants identified at risk of falling completed weekly measures of their physical activity-related cognition and identity; in-depth interviews were completed at course commencement and ten weeks later. During this initial phase of the behaviour change programme, participants developed stronger physical activity identities, with themes reflecting a transition from a physically impaired and negative self to a more future-orientated, capable and integrated self-identity. Concurrently, autonomy-supportive and competence-reinforcing self-talk significantly increased, with non-significant increases and decreases in controlling and amotivational self-talk, respectively. The data suggest that self-talk may be usefully conceptualised as a process through which social messages are interpreted and internalised to integrate a new behaviour into one's existing self-concept.