PIP: The primary source of data for this study of trends in breast feeding among American mothers was Cycle 1 of the National Survey of Family Growth (NSFG) conducted in 1973. Interviews were held with a nationwide, area probability sample of 9797 women aged 15-44 years who had ever been married or who had children of their own living in the household. Study focus was on trends and differentials in the proportion of women who breastfed their babies, not the proportion of babies who were breastfed. With this focus, the findings presented in this report show the comparative frequency with which mothers in different groups have breastfed their infants. Both the NSFG and the 1965 National Fertility Study data show the marked decline in the incidence of breastfeeding in recent generations of American women. Trends by birth cohorts of women show that 2/3 of the women born in the 1920s breastfed their 1st infant, but only 1/4 of the women born in the late 1940s and early 1950s did so. Over 70% of 1st born infants in the 1930s were breastfed, but less than 30% in the late 1960s and early 1970s. The decline leveled off in the early 1970s, but it is too soon to tell if this is an indication of a rise in the rate of breastfeeding. More than 2/3 of the women breastfed their infants in recent years had stopped by the time the child was 3 months old. 2nd born infants were considerably less likely than 1st born to be breastfed. The level and trend in breastfeeding varied widely across various socioeconomic and cultural categories. Among the groups that had experienced the most precipitous declines in breastfeeding levels over the past 2 decades were black women, women with less than 12 years of education, and women who never worked outside the home.