Infant mortality in North-Rhine Westphalia was increased above the national average throughout the postwar period until today. To clarify the underlying causes the official death certificates of infants who died during their first year were linked to their respective birth certificates. Thus, the amount of data about each individual case was increased considerably. The information collected was then evaluated. An especially high mortality was associated with the maternal risk factors illegitimacy, age below 20 and Turkish nationality. Perinatal mortality was high in the groups of Turkish nationals, and unmarried mothers. Socially underprivileged groups on the whole proved to contribute a high amount of postneonatal mortality. Predominant causes of postneonatal mortality were infections, injuries and the diagnosis "sudden infant death syndrome".