The size of a baby’s fontanel (anterior fontanelle) varies according to age and usually closes around 1.5-2 years of age. If the fontanel is still not closed at 2 years of age, it is called delayed closure of the fontanel. A large fontanelle is seen in hydrocephalus, increased intracranial pressure, and premature closure of the fontanelle is seen in microcephaly. The posterior fontanel is small or closed at birth, and closes at the latest at about 6 to 8 weeks of age. The fontanel is about 1 to 2 cm at birth, then increases in size with the growth of the skull, gradually ossifies and becomes smaller at about 6 months of age, and closes by 2 years of age at the latest. Anterior fontanel examination is very important in pediatric clinic, if there is any abnormality, it is usually related to the following factors. 1. Hydrocephalus: A large fontanel with slow closing time is commonly associated with hydrocephalus, which is a delayed and large fontanel closure due to circulatory disorders of the cerebrospinal fluid (CSF) and accumulation of fluid in the brain tissue. 2. Intracranial hypertension: babies with intracranial hypertension due to various reasons can have an enlarged fontanel, such as intracranial space occupation, intracranial hemorrhage, intracranial infection and other diseases. In addition to the enlargement of fontanel, it can also be accompanied by fontanel bulging, increased fontanel tension and other manifestations. 3. Microcephaly: the fontanel closes at the age of 1.5-2 years, and premature closure of the fontanel may affect the brain capacity and development, manifesting as microcephaly, which may be accompanied by abnormal intellectual development. It is recommended to take the baby to the child health department of the hospital on a regular basis to improve the physical examination and monitor the fontanel.