Summary. Infant mortality data in Croatia have been registered in the last 125 years. A tremendous decline has happened during this period from 295,2/1000 live births in 1874 to 7,7/1000 live births in 1999. A tenfold decline was obtained during the second half of the 20th century. In the last years the decline has been slower. Significant differences are found between the counties and also in the counties between different years. Further analysis is needed to make conclusions because the small number of live births influences a lot the infant mortality. During the past period the causes of infant mortality have changed, too. There were classical reasons such as inadequate care about children, low hygienic conditions, poor nutrition, and infectious diseases. Today, causes of infant mortality in Croatia don’t differ from those in developed countries. In the first place are perinatal causes and congenital malformations. The neonatal mortality accounts for 75% of infant mortality. Having in mind current reasons of infant deaths, it is not easy to separate the influences of socio-economical, biological or medical factors. It is particularly impossible to predict the influence of a risk factor on an individual case, because the outcome under the same conditions could be quite different.