Frenotomy of the lingual and maxillary labial frenula in neonates is considered a safe procedure and is increasingly performed globally. However, there is no consistent evidence for the indication and effectiveness of this intervention. In this clinical lesson, we show that frenotomy of the lingual and maxillary labial frenula in neonates is controversial and can have serious complications. We describe a patient that, in addition to pain and the risk of infection, was in a life-threatening haemorrhagic shock after frenotomy of the lingual and maxillary labial frenula. Frenotomy should only be considered after a multi-disciplinary approach of neonates with breastfeeding problems in whom a medical cause is excluded and no contraindications have been identified.