The purpose of this study was to describe the physical activity level of adolescents with cerebral palsy (CP) and to investigate the associated factors. The physical activity level was measured by means of a questionnaire filled in by the parents of 72 adolescents with CP (12–16 years of age) and expressed in METs. Older age, female gender, and hip dysplasia were significantly associated with a lower level of physical activity. Eighty-nine percent were not physically active enough according to the Dutch norm. Physical activity needs to be promoted, especially among older adolescents with CP (age 14–16 years), girls, and adolescents with hip dysplasia.