A 5-level clinical classification system that describes the gross motor function of people with cerebral palsy based on self-initiated movement abilities. People assessed as level I are the most able and people assessed as level V are dependent on others for all their mobility needs. The GMFCS is not validated for use in adults. However, the GMFCS level at age 12 has been shown to be a good predictor of mobility into adulthood, especially at the milder and most severe levels. It is used here in the absence of a validated system for use in adults because it is readily understood by people with cerebral palsy, their families and carers, and health professionals involved in the care of adults with cerebral palsy.