BACKGROUND Cerebral palsy (CP) is the most common cause of motor disability in the paediatric age. For several decades, a number of developed countries have kept registers that have been used to conduct population-based studies of CP. AIM. To determine what methodology is needed to keep a register of CP and in what ways it can be applied. METHODS CP registers came into being as a means to monitor the prevalence of CP. Today they have become useful tools for organising health care services, conducting aetiological studies on CP, evaluating therapeutic interventions and assessing patients' quality of life. Setting up a register involves having an aim and a set of eligibility/exclusion criteria that have both been clearly defined beforehand. The quality of the register depends on its continuity, which means that there must be economic and human resources available to ensure long-term planning and the constant incorporation of new patients. Projects that are coordinated among several centres provide a greater study population and favour the utilisation of a common terminology. CONCLUSIONS The deficits associated to CP, together with its chronicity and the medical, social and educational implications it gives rise to, make it an extremely important health issue today. The ultimate aim of studies on CP should be to improve patients' quality of life and promote their full integration into the world around them.