The aim of the present paper was to verify the basic assumptions underlying the theory of planned behaviour for the prediction of cigarette smoking intentions and behaviour among adults of the general population (study 1) and a group of pregnant women (study 2). Each study was developed based upon Ajzen's theory of planned behaviour. In both studies, baseline data was collected at home with trained interviewers and with the use of paper and pencil questionnaires. The self-report on behaviour was obtained 6 months (study 1) and between 8 and 9 months (study 2) after baseline data collection. In study 1, for smokers, perceived behavioural control, attitudes and subjective norm were explaining intention, whereas perceived behavioural control and habit were the most important predictors of behaviour. In study 2, smoker's intentions was mainly under the influence of perceived behavioural control and attitude, whereas behaviour was predicted by perceived behavioural control only. The present studies suggest that promotional programmes should help smokers to know and develop their will-power regarding non-smoking of cigarettes and should be informed of the effort required in order to modify smoking behaviour.