This study describes the prevalence of adolescent ankle and knee injuries from participation in recreational and sporting activities. Data were collected over a one-week retrospective time frame from 3,538 subjects aged 11-12 years and 15-16 years from the Adelaide metropolitan region. Young people reported participating in 142 recreational activities and, overall, one injury was reported by every fourth subject and in every third activity. Knee and ankle injuries were the most prevalent, reflecting approximately 13 and 14 per cent respectively overall. The most commonly reported activities which had large numbers of knee and/or ankle injuries were investigated in this paper. There were significant differences in risk of ankle and knee injury within age and gender strata for different activities, although similar mechanisms and types of injury were found for both knees and ankles. Strategies to prevent adolescent lower limb sporting and recreational injury are discussed.