In March 1986 five sudden infant deaths were reported, following the diphtheria-tetanus toxoids-pertussis and inactivated poliomyelitis virus (DTP-IPV) immunization of the infants concerned. An epidemiological study was carried out in order to investigate the possibility of a relationship between this immunization and sudden infant death syndrome (SIDS). A detailed examination of the five cases had been carried out by a doctor. An exhaustive survey of all postneonatal deaths occurring between January and March 1986 was conducted and also a matched case-control survey. No significant differences were found in the immunization rates between SIDS and other causes of death, nor between SIDS and living controls. These results are compared with the results from previously published studies on the topic.