Researchers suggest that people with an intellectual disability (ID) undertake less physical activity than the general population and many rely, to some extent, on others to help them to access activities. The Theory of Planned Behaviour (TPB) model was previously found to significantly predict the intention of care staff to facilitate a healthy diet in those they supported. The present study examined whether the TPB was useful in predicting the intentions of 78 Scottish care staff to support people with ID to engage in physical activity. Regression analyses indicated that perceived behavioural control was the most significant predictor of both care staff intention to facilitate physical activity and reported physical activity levels of the people they supported. Attitudes significantly predicted care staff intention to support physical activity, but this intention was not itself significantly predictive of reported activity levels. Increasing carers' sense of control over their ability to support clients' physical activity may be more effective in increasing physical activity than changing their attitudes towards promoting activity.