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), Hon duras (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 < 0.10) with EBF. Women who delivered in the maternity wards that had more developed breast-feeding pro motion programs were more successful with EBF. The association between maternal education and EBF was modified by the maternity ward in Mexico and Hon duras. Being 18 y and having a partner living (Brazil) or not (Mexico) living at home were positively asso ciated with EBF. These findings can contribute toward the design of EBF promotion efforts in Latin America. J. Nutr. 125: 2972-2984, 1995.