This article presents the findings of a population-based cross-sectional survey carried out during a mass immunization campaign. A group of 3,305 mothers whose babies were 0 to 180 days old was selected by systematic sampling and interviewed with a pretested questionnaire. The prevalence of exclusive breast-feeding among 0-15 day-old children was 62% (IC 95%: 58.5-65.3) and 12.8% (11.0-14.7), among 151-180 day-old children. The average duration of exclusive breast-feeding was 39.4 days. The prevalence of predominant breast-feeding was invariable along the age intervals showing a mean of 33.1% (31.4-34.7). The prevalence of partial breast-feeding among 0-15 day-old children was 4.5% (3.1-6.4) and 28.4% (25.8-31.0) for the mentioned age groups. For maternal breast-feeding, the overall prevalence varied from 96.8% (95.8-97.7) to 70.9% (67.7-73.9). In conclusion, although the overall prevalence of breast-feeding in Brasilia is relatively high, the period that children are exclusively breast-fed is short.