Cleft lip is a treatable birth defect of the mouth that appears as one or more splits (clefts) in the upper lip. Cleft lip can range from a small indentation in the lip (incomplete cleft) to a split in the lip that may extend up into one or both nostrils (complete cleft), and possibly into the palate.

Cleft lip forms early in fetal development. The main causes seem to be family history and the mother's health during pregnancy.

Cleft lip often occurs with cleft palate. These conditions are the most common birth defects of the head and neck. Cleft lip, whether it occurs alone or with cleft palate, is more common in males.

Cleft lip is corrected with surgery, usually within the first few months of life. Depending on the type and severity of the deformity, more than one surgery may be needed. Sometimes other treatments, such as speech therapy, are also helpful.