Cerebral palsy (CP) is the commonest disabling impairment in childhood, with a prevalence of 2-3 per 1000 live births. The Danish Cerebral Palsy Registry is a research registry that contains cases of CP from birth year 1925 and has estimated the birth prevalence since 1950. Data on children with CP are collected from paediatric departments and one special institution for disabled children. The children are included by a child neurologist and an obstetrician, and information on pregnancy, birth, neonatal period, impairments and demographic data on the child and mother are registered in a standard form. The uptake area is eastern Denmark, covering about 50% of the population, but the rest of Denmark is planned to be included from 2001. The Registry is large, well established and validated, and the definitions and collection procedures have not changed through several decades. It therefore has great research potential. Birth prevalence is estimated continuously, and changes over time are analysed and correlated with pre- and perinatal conditions. A correlation between increased survival of preterm babies and an increased prevalence was found previously, and a decreased prevalence in very preterm infants was later associated with less use of mechanical ventilation. A study correlating CP and maternal infection is ongoing. Collaboration between 14 European CP registries allows the true differences in prevalence between different countries to be studied. Linkage to other individually based registries in Denmark will allow the social consequences of CP to be described.