Postneonatal deaths in Western Australia from 1970-78 were studied using a linked file of birth and death registrations. Postneonatal mortality fell during the period under study. The fall occurred in both male and female rates and the former were higher than the latter in all years. The infants at high risk during the postneonatal period were those born to unmarried teenage mothers residing in rural areas, especially if the infants were of low birthweight (less than 2500g). Multiple births and those infants born to mothers whose previous issues were over 4 were also at high risk. Infants born to Aboriginal mothers experienced a significantly higher rate of postneonatal mortality than those born to non-Aboriginal mothers. However, a significant improvement in the Aboriginal rate occurred between 1976 and 1977. The major causes of postneonatal death were sudden infant death syndrome, infections and congenital abnormalities.