The infant mortality rate has declined dramatically in Peninsular Malaysia since World War II. This study uses individual-level retrospective data on infant mortality and its correlates (from the Malaysian Family Life Survey) to examine possible reasons for this decline. One important factor has been the substantial increase in mothers' education. Improvements in water and sanitation also played a role. However, the reductions in breastfeeding that have taken place in Malaysia have kept the infant mortality rate from declining as rapidly as it would have otherwise. In this analysis, the detrimental effects of reduced breastfeeding have more than offset the beneficial effects of improvements in water and sanitation. The majority of the infant mortality decline, however, is not explained by changes in the variables considered here, but is due to factors not investigated here — most likely, improvements in medical and health care.