Background Smoking is one of the risk behaviours that begin in adolescence, and therefore identifying predictors of smoking is necessary for planning prevention programmes.

Objectives To examine the ability of the extended theory of planned behaviour (TPB) to predict the intention to smoke.

Methods This was a cross-sectional study carried out in Iran, 2011. The data were collected by a self-administered questionnaire which included items on demographics, smoking behaviour, components of the TPB model (attitude, subjective norms, perceived behaviour control and intention) and an added construct on smoking self-identity. Data were analysed using descriptive, correlation and linear regression statistics.

Results 365 male high school students with a mean age of 16.5 (SD=1.2) years were studied. Fifty-five (15.1%) of the students surveyed were current smokers. All components of the TPB model and smoking self identity were statistically significantly related to intention to smoke (p<0.001). The TPB constructs with and without smoking self-identity accounted for 58.5% (adjusted R²) and 54.8% of the variance observed for intention to smoke, respectively. Result also revealed the highest weights for perceived behaviour control (β=−0.35).

Conclusions The extended model of the TPB predicted ‘intention to smoke’ better than the original TPB. The findings of this study might be used as a framework in designing heart disease prevention programmes. Thus the findings have implications for both health promotion specialists and cardiologists. They could place an emphasis on perceived behaviour control, specifying that individuals who do not smoke should not start and if they are smokers it is possible to stop smoking.