Study of the postperinatal infant mortality offers certain advantages for international comparison, because the problems of differences of definition and confusion between stillborn and liveborn infants are largely eliminated. Furthermore, the postperinatal rates concentrate on the area in which environmental influences and the quality of care given the infant are predominant. Data available for comparison of rates between 1956 and 1966 suggest that while there are wide variations internationally, some countries with very high rates have been able to improve dramatically. Most countries with rates between 15 and 50 have improved substantially and a large proportional improvement occurred even among countries with quite low rates. In the latter group the position of the United States has become substantially worse in the decade under study.