Purpose To analyze the influence of ankyloglossia on the prevalence and duration of exclusive breastfeeding of full-term infants up to the sixth month of life. Methods Prospective cohort study, carried out with 225 mother-infant dyads who were followed up in the first six months of life in a center specialized in breastfeeding in a tertiary hospital. Full-term infants with asymptomatic ankyloglossia (no need for surgery) were compared with infants without change at monthly follow-up. Ankyloglossia was diagnosed using the Bristol Tongue Assessment Tool, with a positive diagnosis being considered for those with a score less than or equal to 5 considering functional and anatomical aspects. Statistical analyzes were performed using descriptive statistics, logistic regression (weaning determinants), relative risk, and survival curves (to analyze breastfeeding duration between groups with and without ankyloglossia). Results Ankyloglossia was associated with weaning (considered even partial) before the sixth month of life. After adjusted analysis, a higher risk of weaning was detected in infants with this alteration, with a risk present from the second month of life. In the survival analysis, the duration of breastfeeding in infants with ankyloglossia was shorter when compared to children without alterations. Conclusion Compared to infants with normal lingual frenulum, babies with ankyloglossia had shorter exclusive breastfeeding time, but well above the average observed in the general population. The risk of weaning for this group was also higher.