The aim of this study was to evaluate the incidence, nature, and risk factors of unintentional injuries among 12-, 14-, 16- and 18-year-old Finnish adolescents. Of the 8219 respondents (response rate 75%) 5.5% reported an injury that had required medical attention during the past month. The total number of injuries was 506 and the incidence of injuries 62 per 1000 person-months. Boys had a slightly higher injury occurrence rate than girls (OR: 1.33; 95% CI: 1.13-1.59). The most common injuries were sprains (27%), fractures (26%) and wounds (16%) of the upper and lower limbs. In multivariate logistic regression analysis the strongest risk factors of injury were: having experienced violence during past month (OR: 3.6; 95% CI: 2.8-4.6), daily leisure time exercise in sports club (OR: 3.3; 95% CI: 2.3-4.6), having several somatic health complaints weekly (OR: 2.2; 95% CI: 1.7-2.9) and having chronic disease (OR: 2.0; 95% CI: 1.5-2.6). In conclusion, injuries were an important cause of morbidity among our 12-18-year-old adolescents. Adolescents' school success and their parents' education, occupation and employment status were not associated with injuries. The finding that several health and health behaviour variables are important risk factors for injuries challenges the researchers and the society to identify and treat the risk factors that can be modified to reduce the number of adolescent injuries.