BACKGROUND: Physical activity is generally accepted as a healthy habit. Nevertheless, its associated risk to cause injuries has not been sufficiently evaluated. Measuring this risk more precisely would contribute to giving more accurate health advice to the general population. METHODS: Data are from participants (60% women, mean age 38 years) in a cohort of university graduates in Spain (1999-2008). Among other exposures and outcomes, they self report on frequency of participation in several physical activities over 1 year, and on incidence of sports-related injuries after 2, 4 or 6 years follow-up. Participation in 17 physical activities was categorized as a dichotomous variable (yes/no) and also according to average time per week spent in each one. Proportional hazards regression was used to estimate the adjusted relative risks [hazard ratios (HRs)] of incident injury associated with each specific physical activity or with total weekly energy expenditure in leisure-time activity [metabolic equivalents (METs)-h/week]. Statistical analyses were stratified by sex. RESULTS: We identified 1658 incident sports-related injuries among 14 356 participants after a median follow-up of 4.6 years. When we adjusted for overall energy expenditure (METs-h/week) in other activities, age and body mass index (BMI), a higher risk of injury was associated with participation in soccer, other team sports, skiing, tennis, running and athletics (HRs ranging from 1.50 to 1.86) among men. With the exception of soccer (rarely practiced by women in Spain), similar results were found for women (HRs ranging from 1.61 to 2.04). Walking, gymnastics, swimming, mountain hiking and gardening were associated with a low injury risk. CONCLUSIONS: Despite the healthy effects of physical activity, we consider that the higher risk for injuries related to soccer, team sports, skiing, tennis, running or athletics should be taken into consideration when advice for more physical activity is given to the general population. Daily routine physical activities such as walking or gardening should be encouraged.