Purpose to evaluate the introduction of pacifiers in children assisted by an interdisciplinary program of encouraging breastfeeding during the first six months of life, investigating the possible determinants of their use. Methods a descriptive, exploratory, longitudinal, quantitative study, through monitoring of 120 mothers and their children. Data were collected on personal characteristics, and demographic variables related to pre-, peri-and postnatal. Bivariate analysis were performed by Chi-square and Fisher exact test and multiple regression analysis with robust adjustment Poisson standard error. Results the analysis revealed that 13.33% of children using pacifiers at the end of the first month of life and 23.33% had this habit at the end of the sixth month. Pacifier use was positively associated with lack of exclusive breastfeeding for the first month (PR: 5.44, CI95%:2.38-12, 44). At the end of the sixth month, this habit was associated with absence of exclusive breastfeeding at discharge from hospital (PR: 4.91, CI95%:1.79-13, 48) and lack of exclusive breastfeeding at six months of life (PR: 2.32, CI95%:1.32-4, 08). Conclusion the use of pacifiers during the first six months of life for children assisted by a program to promote breastfeeding was associated with lack of exclusive breastfeeding.