Adventure-physical education has been proposed to promote adolescents' physical development, but little is known about physical activity levels during such lessons. Using the System for Observing Fitness Instruction Time, we observed students' (ages 11-14 years) physical activity levels in co-educational classes during 43 adventure-physical education lessons at seven public schools. The mean percentage ([plus or minus]SD) of time spent in moderate-to-vigorous physical activity (MVPA) was 28.3% ([plus or minus]16.3%). The greatest percentage of lesson time was spent in two activities--high elements (24.1% [plus or minus] 36.5%) and initiatives (22.3% [plus or minus] 32.4%). When data were aggregated across all lessons, 40.0% of the time in high elements and 13.7% of the time in initiatives was spent in MVPA. Of all MVPA time, 31.5% occurred in high elements and another 12.6% in initiatives. Compared with traditional physical education lessons, less time is spent in MVPA during adventure lessons. Efforts to increase MVPA should target high elements and initiative activities. (Contains 4 tables.)