The aim of the study was to describe daily physical activity levels of adolescents and young adults with bilateral spastic cerebral palsy (CP) and to identify factors that help predict these levels.Daily physical activity was measured using an accelerometer-based activity monitor in 45 young people with bilateral spastic CP (23 males, 22 females; mean age 18y 6mo [SD 2y 5mo] range 16y 1mo-20y 11mo); classified as Gross Motor Function Classification System (GMFCS) level II or III and with contractures of <20° at hip and knee. Predictor variables included demographic characteristics (age, sex, weight) and physical characteristics (gross motor function, lower limb muscle strength, 6min walk distance). Data were analyzed using the information-theoretic approach, using the Akaike information criterion (AIC) and linear regression.Daily activity levels were low compared with published norms. Gross Motor Function Measure Dimension-E (GMFM-E; walking, running, and jumping) was the only common predictor variable in models that best predicted energy expenditure, number of steps, and time spent sitting/lying. GMFM Dimension-D (standing) and bilateral reverse leg press strength contributed to the models that predicted daily physical activity.Adolescents and young adults with bilateral spastic CP and mild to moderate walking disabilities have low levels of daily activity. The GMFM-E was an important predictor of daily physical activity.