Only limited research has been conducted on the patterns and determinants of changes over time in the extent and duration of breast-feeding. Methods are used that allow the examination of the effects of changes in population characteristics and behavioral factors on breast-feeding outcomes. Comparable national surveys are employed to examine the factors associated with the combination of a decline in the extent of and an increase in the duration of breast-feeding between 1973 and 1983 in the Philippines. Important differences are found in the factors explaining the extent and duration of breast-feeding between 1973 and 1983.