In 1986 The Office of Population Censuses and Surveys (OPCS) introduced new certificates for stillbirths and neonatal deaths. This allowed certifiers more flexibility in the completion of the certificate, and the number and ordering of the causes given. Tabulations have been published of the fetal and maternal causes of death mentioned on the certificates for every year from 1986 to 1991 in annual reference volumes. It has not been possible either to derive a single cause group for each death, however, or to compare the information available on neonatal deaths with that on postneonatal deaths, which are still derived from the standard death certificate. The aim of the work described here was to adapt previous classifications to derive a single cause grouping for stillbirths and infant deaths which would provide the maximum information about preventability and yet meet the national and international responsibilities of OPCS. The methods used and the tests carried out on the validity and consistency of the chosen classification are described.