Our objective with this article was to describe the declining trend in neonatal mortality in Chile between 1990 and 2000 and examine potential causal factors. Descriptive analysis of data that were provided by the Chilean Ministry of Health on all approximately 2,900,000 births occurred in Chile between 1990 and 2000. Total neonatal mortality rates (<28 days), and birth weight-specific and gestational age-specific mortality rates from 1990 to 2000 were analyzed by year. Public health interventions that were implemented during the 1990s were reviewed to assess their potential influence on the observed trends in neonatal mortality. The neonatal mortality rate between 1990 and 2000 decreased from 8.3 to 5.7 per 1000 live births. This decline was not associated with decreases in the proportion of low birth weight and preterm infants but rather with declines in birth weight-specific and gestational age-specific mortality rates. Examination of the trends in birth weight-specific and gestational age-specific mortality rates showed that a marked proportional decrease in mortality rates was achieved among infants who weighed <1500 g and were delivered before 32 weeks. It is plausible, both biologically and temporally, that the observed trends in the reduction in birth weight-specific and gestational age-specific mortality rates are associated with the introduction of specific sector-wide interventions that aim to improve newborn care in very preterm and low birth weight infants. Important reductions in newborn mortality in developing countries are possible with the implementation of effective neonatal care interventions.