An examination of the recent decline in perinatal mortality in Scotland during the 1970s showed that despite substantial changes in fertility and the demographic pattern of births, differences in the age, parity, and social class composition of the obstetric population in this decade accounted for just 7% of the overall improvement in perinatal mortality between 1970 and 1979. The general pattern of relative risks associated with maternal age, parity, and social class remained largely unchanged. Marginal changes in the birthweight distribution, however, were sufficient to account for 13% of the reduction in perinatal mortality. The low birthweight infant, especially those weighing under 1500 g, assumed increasing importance as a factor in perinatal mortality owing to a progressive worsening in the relative risk of perinatal mortality associated with low birth weight. Although regional differences in perinatal mortality persisted over this period, there occurred some lessening of the traditional inequality between western and eastern parts of the country. Finally, registered causes of perinatal mortality are reviewed. In the absence of other explanations the results of this analysis, collectively, suggest that much of the recent decline in perinatal mortality was perhaps due to changes in obstetric practice and in the clinical management of neonatal morbidity.