Background: School accidents in adolescents in professional and technological secondary schools are relatively frequent. This work investigates these accidents in Lorraine (a French region) to identify preventive measures., Methods: A cross-sectional study was carried out in 4,751 adolescents from five volunteering schools. Only accidents occurring during one school-year and declared to the Social Security Services as work accidents were studied., Results: Incidence of accidents per 1,000 subjects was 52.0: 21.3 for accidents during sports and physical training (SPT), 7.8 for those occurring during school training (except SPT), and 22.9 for spare time accidents. The incidence increased strongly with age and differed greatly between the type of schools. Girls had more accidents during SPT than boys. Injuries during school training were wounds and contusions of upper limb while the injuries during SPT and spare time were mainly articular disorders, contusions, and wounds of the upper limb, the lower limb, and the head and neck. A physician was consulted in almost 100% of the injuries, a radiological examination was performed for 75%, and a surgical intervention for 14% of the injuries. Absence from school, exemption from workshops and from SPT were frequent. The predominant risk factors were the type of activities, especially activities the adolescents were not accustomed to, personal behavior and risks taken by adolescents., Conclusion: Accidents are frequent, in particular among older adolescents. It is important to identify activities at risk, and to target prevention and awareness campaigns, assessment training to evaluate risks of each activity, and promoting safe behavior, although environmental factors cannot be excluded.