AIM To examine tobacco use among teenagers, identify factors related to tobacco use, as well as evaluate the outcome of a smoking prevention program. METHODS From age 7/8 to 14/15, annual questionnaires about asthma and allergy have been completed in the OLIN paediatric study in Northern Sweden. From 12/13 years, questions about tobacco use, i.e. smoking and snuff, were added. A smoking prevention program was performed during 2 years. RESULTS Any tobacco use increased from 5.0% at age 12/13 years, to 14.4% at age 14/15. At age 14/15 years, the prevalence of tobacco use was significantly higher among boys than girls (16.7 and 12.0%, respectively). More girls than boys smoked (8.9 and 2.8%, respectively), while use of snuff was more common among the boys (15.6 and 4.2%, respectively). Significant risk factors for smoking were any of the family members currently smoking, OR 6.1 (95% CI 4.0-9.3) and a physician-diagnosed asthma at the age of 14/15 years, OR 1.9 (95% CI 1.2-3.0). A protective factor against tobacco use was participation in sports, OR 0.3 (95% CI 0.2-0.4). The prevention program did not result in less tobacco use, although it may have delayed smoking initiation. CONCLUSION The patterns of tobacco use differed significantly between boys and girls. Though any tobacco use was more common among boys, girls were more likely to smoke, and boys were more likely to use snuff. Having asthma did not prevent the teenagers from smoking. Since having a smoking family member was the major risk factor for tobacco use, prevention programs should be directed at smoking families in addition to the individuals.