['To describe the rate of and demographic factors associated with fetal postmortem investigation and to classify the cause of all fetal deaths that underwent postmortem investigation. To compare the proportion of deaths remaining unexplained after postmortem investigation with estimates derived from death certificates.', 'All fetal deaths in Western Australia (WA) from 1990 to 1999 were identified. These data were used to calculate postmortem rates and describe the characteristics of women consenting to postmortems. A multidisciplinary team classified the cause of all deaths that underwent postmortem investigation using the Perinatal Society of Australia and New Zealand Perinatal Death Classification System. The proportion of deaths that were unexplained was compared with estimates based on death certificates.', 'Of the 1,619 fetal deaths recorded for 1990 to 1999, 49% (n=789) underwent complete postmortem investigation. Based on investigations, 22% of the 789 fetal deaths were unexplained and a further 18% were identified as having fetal growth restriction. Based on death certificates, 42% were unexplained and 65% were later explained by postmortem investigation.'] Is aetiology of stillbirth : unexplored unexplained?