A regional register of preschool children with cerebral palsy, severe vision loss and sensorineural deafness has been complied. Case definition, the threshold for including or excluding a case and a standard method for describing a case have been predefined. In order to achieve complete ascertainment, multiple sources of information were used and account was taken of population movement, and loss of cases through death. The optimal age of case ascertainment poses a particular problem and counting of definite cases was delayed until age three years with a further review at age five years. The register can be used to estimate prevalence of impairment, as a basis for aetiological and interventive studies and for service planning. It fills an important gap in the information currently available on childhood morbidity.