The commonest deformity of the PALATE is cleft palate, which is a result of faulty embryonic development in which the two sides of the newly-forming palate fail to join, completely or partially. If the cleft extends the full length with bilateral clefts at the front of the MAXILLA, it may be accompanied by a cleft lip (also called hare-lip) and disruption in the development of the front teeth. About 1 in 500 babies is born with a cleft lip and 1 in 1,000 has a cleft palate. If the parents are affected, the risk is three times that of the normal population; if one child has a deformity, the risk for a subsequent child is higher. Associated abnormalities include tongue tie, malpositioning of the MANDIBLE and fluid in the middle EAR.

Cleft palate and hare-lip are rectified by operation, because both are a serious drawback to feeding in early life – while later, hare-lip is a disfigurement, and speech is affected. The lip may be dealt with at any time from the neonatal period to a few weeks, depending on the individual surgeon's view of when the best result is likely to be achieved. Before operation, special techniques may be necessary to ensure adequate feeding, such as the use of special teats in formula-fed babies. The closure of a large cleft in the palate is better performed when the face has grown somewhat, perhaps at 6–12 months. The operations performed vary greatly in details, but all consist in paring the edges of the gap and drawing the soft parts together across it.

Further operations may be required over the years to improve the appearance of the nose and lip, to make sure that teeth are even, and to improve speech.