The association between breast feeding duration in two consecutive pregnancies was studied in a prospective study in southern Brazil. In a population-based sample of 5960 women giving birth in 1982, 1386 delivered a second child within 4 years. The data were analyzed using life table techniques. The duration of breast feeding of the second child increased directly according to the duration the previous child had been breast fed. In particular, when the previous child had been breast fed for 6 months or more, the subsequent child was clearly more likely to be breast fed. However, when the previous child had been breast fed for under 6 months, the differences among subsequent children disappeared after 3-6 months. These differences were still present after stratification by family income, maternal education and parity. Mothers with a previous unsuccessful or problematic breast feeding experience should receive special priority in promotion campaigns.