ABSTRACT Purpose To analyze the association between ankyloglossia and breastfeeding. Methods A cross-sectional study was undertaken on 130 newborn infants in exclusive breastfeeding with Apgar score ≥ 8 within the first five days of life. The research was approved by the Ethics Committee on Human Research. The data collection was performed by the researcher and by three trained speech therapists of the team. The protocols applied were the Neonatal Tongue Screening Test from the Lingual Frenulum Protocol for Infants, the UNICEF Breastfeeding Observation Aid, and the collection of maternal complaints related to the difficulty in breastfeeding was also considered. The data were submitted to statistical analysis – chi-square test and Fisher’s exact test, with a significance level of 5%. Results When correlating the data, the statistical analysis revealed an association between ankyloglossia and the items of suckling category of the Breastfeeding Observation Aid. The association between complaint of difficulty in breastfeeding and ankyloglossia was also seen. Conclusion On the first days of life, ankyloglossia is associated with the mother’s breastfeeding complaint and with the newborn’s sucking difficulty.