The knowledge and beliefs about smoking of smokers, non-smokers, and ex-smokers were examined within a cognitive dissonance framework. The 186 respondents completed a questionnaire concerned with smoking habits, knowledge of the effects of smoking, beliefs about smoking, and estimates of risk of lung cancer to themselves and to the average Australian smoker. Smokers estimated their risk of contracting lung cancer as greater than the risk non-smokers or ex-smokers saw for themselves, but less than the risk for the average Australian smoker. No differences were found in the amount of factual knowledge about the effects of smoking. However, smokers endorsed significantly more rationalisations and distortions of logic regarding smoking than did non-smokers or ex-smokers. Smokers may experience cognitive dissonance as a result of using tobacco despite its well-publicised ill-effects, and it may be that interventions targeting rationalisations for smoking will be useful in smoking cessation.