PIP: International differences in trends in postneonatal mortality are reviewed and some of the data available for interpretation of these trends are examined. An earlier review of perinatal and infant mortality examined the trend in the countries of Denmark, England and Wales, the Netherlands, Norway, Scotland, Sweden and the United States over the 1935 to 1964 period. These earlier data are expanded to include the countries of Australia, New Zealand, Japan, Finland, France, the Federal Republic of Germany and Switzerland. Since 1945 several countries have shown an initial rapid rate of decline in postneonatal mortality followed by a period of much slower decline. In the United States, the plateau was followed by a more rapid decline post-1965. In England and Wales and Scotland, the plateau persisted for a longer time than in the U. S. Since 1973 a period of rapid decline is again evident, which is even more pronounced in Scotland than in England and Wales. Denmark, the Netherlands and Sweden all have consistently low rates of postneonatal mortality subject to annual fluctuation which makes interpretation of the overall trend more of a problem. The Federal Republic of German and Norway show a recent deterioration in postneonatal mortality. The primary factor in the falling postneonatal mortality rates in the 20th century has been the gradual abolition of deaths due to infections. Countries with the lowest postneonatal mortality rates show an insignificant number of such deaths, with congenital malformations now in 1st place. The disproportionate contribution of young mothers with large families and in poor social situations to postneonatal mortality raises the question of how much demographic changes are involved in mortality improvement.