Patterns of breastfeeding were studied in a cohort of 5 914 infants followed from birth in Pelotas, Southern Brazil. Overall, 92% of the babies commenced breastfeeding and 54% were still breastfed by 3 months of age. This proportion dropped to 30% by 6 months, 20% by 9 months, and 16% by 12 months. The prevalence of breastfeeding soon after birth, and at 3, 6, 9 and 12 months of age was studied according to socioeconomic status as measured by family income. Children from the poorest families were less likely to be breastfed from birth than those from the richest families (89% and 97%, respectively), and also showed lower prevalence of breastfeeding at 3 and 6 months. By the age of 12 months poor children showed the highest prevalence of breastfeeding.