Data on breastfeeding were compared for two population-based cohorts of children born in 1982 and 1993 in the city of Pelotas in southern of Brazil. All hospital births taking place in both years were studied and samples of these children were visited at home at around 12 months of age. The median duration of any breastfeeding increased from 3.1 to 4.0 months in this period. In the first months, breastfeeding was more prevalent in high-income families, but from nine months onwards it was commoner among the poor. Low birthweight babies had shorter breastfeeding durations. Bernardo Lessa Horta e-mail [log in to unmask]