Background: The majority of observational studies have found associations between pacifier use and shorter breastfeeding duration. Results from four randomised controlled trials did not reveal any difference in breastfeeding outcomes. The relationship between early pacifier use and breastfeeding outcomes remains unclear. Aim: To investigate whether a recommendation of early pacifier use affects the proportion of breastfeeding at six months compared to a recommendation to avoid pacifier use during the first two weeks. Methods: An open, randomised controlled trial with parallel group design; 239 primiparous mothers and their term infants were randomly assigned to an intervention group or a control group. The primary outcome was the proportion of breastfeeding at six months. Secondary outcomes were the proportions of breastfeeding and breastfeeding problems at two and four months. To investigate factors which may influence breastfeeding, a multivariate logistic regressions analysis was performed. Findings: A total of 209 participants (87.5%) completed the study. There were no significant differences between the groups with respect to breastfeeding at six months. No negative association for breastfeeding between early versus late introduction of pacifier was found. Factors significantly associated with cessation of breastfeeding at six months were: use of nipple shield, intention to breastfeed, severe breastfeeding problems at two weeks, pacifier use at two months and lower educational level. Conclusion: Early versus late recommendation of pacifier introduction did not affect the proportion of breastfeeding at six months. However, the compliance to the randomised group was insufficient. No negative association was found in the observational analysis. (C) 2019 Australian College of Midwives. Published by Elsevier Ltd. All rights reserved.