Background: To explore the factors predicting preventive behaviours among NHS dentists in Camden, Islington and Haringey in London, using constructs from the Theory of Planned Behaviour. Methods: A cross-sectional survey of NHS dentists working in North Central London was conducted. A self-completed questionnaire based on the theoretical framework of the Theory of Planned Behaviour was developed. It assessed dentists' attitudes, current preventive activities, subjective norms and perceived behavioural control in delivering preventive care. In model 1, logistic regression was conducted to assess the relationship between a range of preventive behaviours (diet, smoking and alcohol) and the three TPB constructs attitude, subjective norms and perceived behavioural control. Model 2 was adjusted for intention. Results: Overall, 164 questionnaires were returned (response rate: 55.0 %). Dentists' attitudes were important predictors of preventive behaviours among a sample of dentists in relation to asking and providing diet, alcohol and tobacco advice. A dentist was 3.73 times (95 % CI: 1.70, 8.18) more likely ask about a patient's diet, if they had a positive attitude towards prevention, when adjusted for age, sex and intention. A similar pattern emerged for alcohol advice (OR 2.35, 95 % CI 1.12, 4.96). Dentists who had a positive attitude were also 2.59 times more likely to provide smoking cessation advice. Conclusions: The findings of this study have demonstrated that dentists' attitudes are important predictors of preventive behaviours in relation to delivery of diet, smoking and alcohol advice.