Few studies describe the factors associated with smoking behaviour in Portuguese adolescents. Hence, smoking prevention activities are not based on research findings. This study analyses the differences between smokers and nonsmokers and factors associated with smoking behaviour in a sample of Portuguese adolescents. A questionnaire was administrated to seventh grade students of 25 schools from five municipalities near Lisbon (n=3064). The majority of them were never smokers (71.3%), 21.9% smoked less than monthly, 2.1% monthly and 4.7% weekly or more frequently. Smokers were older, had lower school achievement, had more money available to spend, preferred less to be together with nonsmoking people and were more likely to be allowed to smoke at home, to use alcohol and to perform various risky behaviours. Nonsmokers were less convinced of the advantages and more convinced of the disadvantages of smoking, encountered more social norms against smoking, perceived less smoking in others, felt less pressure to smoke from peers, were more confident to refuse cigarettes and had a lower intention to smoke next year. Intention to smoke, self-efficacy expectations to refuse smoking, social influence and alcohol consumption were the most relevant variables associated with smoking behaviour. Consequently, Portuguese smoking prevention programmes should include activities aimed to help adolescents to deal with pressure to smoke from peers and to improve self-efficacy expectations to refuse cigarettes. Our findings also confirm the link between smoking and alcohol use suggesting that the prevention of these two behaviours should be complementary.