Children with severe cerebral palsy (CP) are at high risk for progressive hip displacement, associated with pain and contractures interfering with many aspects of care, comfort and quality of life. These children undergo many types of interventions, the optimal timing and effectiveness of which, remain unclear. In 2014, CIHR funded the CP Hip Outcomes Project (CHOP), an international multi-centre prospective longitudinal cohort study of children with severe (non-ambulant) CP with evidence of hip displacement defined as a Reimer's migration percentage (MP) of at least 30%. The study was designed to evaluate the comparative effectiveness of different treatment strategies to prevent or relieve symptoms associated with hip instability, using the validated Caregiver Priorities and Child Health Index of Life with Disabilities (CPCHILD ) questionnaire as the primary outcome measure of health-related quality of life © (HRQL) for this population. 650 patients enrolled from 28 sites in 11 countries, are actively being followed and will reach at least 2 years of follow-up at the end of 2019. This project, will study the impact of hip instability and its management in children with severe CP using the CPCHILD questionnaire that was developed specifically for this purpose. Although CHOP will define outcomes at 24 months, the outcomes are not expected to remain stable while the child is still growing. The inception cohort will need follow-up until skeletal maturity to track their long-term outcome trajectories.