Breastfeeding is fundamental for infant health. However, its median duration in Brazil is very short, and national campaigns since the mid-1980s have attempted to revert this situation. In the present paper, data on breastfeeding are compared for two population-based cohorts of children born in 1982 and 1993 in the city of Pelotas in Southern Brazil. All hospital births in both years were studied and samples of these children were visited at home around 12 months of age. Median duration of breastfeeding increased from 3.1 to 4.0 months in this period. This rise suggests an impact by the national campaigns. In both cohorts, there were interactions between family income and the percentages of children breastfed at different ages. In the early months, breastfeeding was more prevalent in high-income families, but from nine months onwards it was more common among the poor. Low birthweight babies enjoyed shorter duration of breastfeeding. Despite the progress observed during the decade, duration of breastfeeding is still far short of international recommendations, justifying further campaigns prioritizing low birthweight babies and those from low-income families.