Abstract
Data on all livebirths and infant deaths occurring to residents in Belfast 1963-5 and in Birmingham 1964 were analysed in order to examine possible reasons why the infant mortality rate in Belfast (29·4 per 1000 livebirths) was higher than in Birmingham (21·4). The hypothesis that the excess infant mortality in Belfast was mainly due to a higher proportion of infants born to high parity Belfast mothers was tested and found to be untenable. Though significant differences between the distributions of livebirths by parity in the two cities were demonstrated, they could have accounted for only about 12% of the excess. Differences between the two livebirth distributions by birthweight were more important and accounted for 40% of the excess infant mortality in Belfast. A high mortality rate attributed to postnatal asphyxia and atelectasis (I.C.D. No. 762) was noted in this city.