Abstract: We explored the role of exercise self-identity within the framework of the theory of planned behaviour (TPB). Participants were 538 undergraduate students who completed measures of exercise self-identity, exercise behaviour, TPB items and behavioural and control beliefs. Regression analysis showed that self-identity was the second strongest predictor of exercise behaviour and interacted with exercise intention. Follow-up analysis showed that the intention-exercise relationship was more than three times stronger at high levels of exercise self-identity that a low levels. Results also showed that only a marginal part of the sample with strong exercise identities had a weak exercise intention, whereas a large part of the sample with a strong exercise intention also reported a strong exercise identity. Nevertheless, only a quarter of the sample that reported strong exercise identity and intention were sufficiently active. The results underline the notion that exercise self-identity may be a useful component for the theory of planned behaviour.