Infant mortality in a region of Finland with about 450,000 people and 5400 annual births was examined during a 15-year period, 1968-1982. Total infant mortality declined from 15.8 per 1000 live births in 1968 to 5.0 in 1982. The lowering of neonatal mortality accounted for the decline, as postneonatal mortality remained at the same level throughout the study period. Despite a decrease of nearly 80%, perinatal disorders remained the leading category of primary causes of death. Mortality from congenital malformations decreased by 50%, mortality from sudden infant death syndrome increased from 0.2 to 0.9 per 1000 live births while mortality from accidents, infectious diseases and other diseases remained minor causes of death with no change in frequency. In the low birth weight category, postponement of deaths from early to late neonatal and postneonatal periods occurred, but total infant mortality in the low birth weight category declined by about 60%. During the last two 3-year periods, decrease in birth weight-specific infant mortality was found in the 500-999 g and greater than 2500 g categories. The reasonably high standard of living, good educational level of mothers, well organized primary maternal and child health services and the rapid advances in obstetric and neonatal care equally available and regionalized, have contributed to the favourable progress in infant mortality in Finland.