OBJECTIVES: To study how individual and regional characteristics might explain regional variations in breast-feeding rates in maternity units and to identify outlier regions with very low or high breast-feeding rates. DESIGN: Individual characteristics (mother and infant) were collected during hospital stay. All newborns fed entirely or partly on breast milk were considered breast-fed. Regional characteristics were extracted from census data. Statistical analysis included multi-level models and estimation of empirical Bayes residuals to identify outlier regions. SETTING: All births in all administrative regions in France in 2003. SUBJECTS: A national representative sample of 13 186 live births. RESULTS: Breast-feeding rates in maternity units varied from 43 % to 80 % across regions. Differences in the distribution of individual characteristics accounted for 55 % of these variations. We identified two groups of regions with the lowest and highest breast-feeding rates, after adjusting for individual-level characteristics. In addition to maternal occupation and nationality, the social characteristics of regions, particularly the population's educational level and the percentage of non-French residents, were significantly associated with breast-feeding rates. CONCLUSIONS: Social characteristics at both the individual and regional levels influence breast-feeding rates in maternity units. Promotion policies should be directed at specific regions, groups within the community and categories of mothers to reduce the gaps and increase the overall breast-feeding rate.