Current breastfeeding patterns in the City of Sao Paulo were determined from a random sample of 1016 children under 5 years of age between 1984 and 1985. Although breastfeeding is started for the majority of children its medium duration does not exceed 4 months for overall breastfeeding and about 2 months for exclusive breastfeeding. Unlike the patterns usually found in developing countries the rates of breastfeeding during the 1st 6 months of life are significantly higher among the high socioeconomic strata in whom rates for exclusive breastfeeding are particularly impressive. Certain characteristics of local public health services such as the extremely high incidence of deliveries by caesarean section (47.3% of all deliveries) virtual non-existence of rooming-in and indescriminate distribution of powdered milk to children under 1 year of age could explain in part the high incidence of early termination of breastfeeding. The direct association between breastfeeding and socioeconomic status may have been determined by a greater impact of the national breastfeeding campaign since 1981 on mothers in this social group. (authors modified)