PURPOSE: to determine the influence of received guidance about breastfeeding on the knowledge and practices of mothers attending a university hospital. METHODS: descriptive observational study conducted with 250 mothers, aged between 18 and 45 years, who were in the Phonoaudiology Clinic for conducting newborn hearing screening and had their babies no later than six months ago. These mothers, who were previously oriented or not, answered a questionnaire about breastfeeding. RESULTS: mothers who received previous guidance showed greater knowledge about: the appropriate age to offer other foods (p = 0.001), the utensils used for food (p = 0.031), the disadvantage of bottle-feeding (p = 0.037) and pacifier (p = 0.019). Only mothers guided both on pre and post-natal reported using a syringe for feeding (p = 0.045). Moreover, the percentage of mothers who breastfeed on demand and new how to store milk was higher among those who had received guidance on the subject (p <0.001 and p = 0.027). The preparation of the breasts was best performed by mothers not previously guided (p = 0.002). CONCLUSION: this study showed that receiving guidance on breastfeeding did not determine greater knowledge on the subject, emphasizing the need of having a multidisciplinary team working in guidance of mothers as well as the importance of participation of the phonoaudiologist, who is the qualified professional to address issues of prevention of orofacial disorders.