International health organizations have recommended exclusive breast-feeding (EBF) (i.e., breast milk as the only source of food) as the optimal infant feeding method during the first 4-6 mo of life. Therefore, it is important to document the determinants of EBF in different populations. Low-income urban women from Brazil (n = 446, 2 maternity wards), Honduras (n = 1582, 3 maternity wards) and Mexico (n = 765, 3 maternity wards) were interviewed at birth and in their homes at 1 mo and 2-4 mo after delivery. Multivariate survival analyses (Cox model) indicated that planned duration of EBF (all 3 countries), having a female infant, and not being employed (Brazil and Honduras), lower socioeconomic status (Honduras and Mexico) and higher birth weight (control hospital in Brazil and Honduras) were positively associated (P < or = 0.10) with EBF. Women who delivered in the maternity wards that had more developed breast-feeding promotion programs were more successful with EBF. The association between maternal education and EBF was modified by the maternity ward in Mexico and Honduras. Being > or = 18 y and having a partner living (Brazil) or not (Mexico) living at home were positively associated with EBF. These findings can contribute toward the design of EBF promotion efforts in Latin America.