A risk factor is anything that increases a person's chance of developing a tumor. Although risk factors often influence the development of a tumor, most do not directly cause a tumor. Some people with several risk factors never develop a tumor, while others with no known risk factors do.

The cause of most CNS tumors in children is not known. Researchers are studying a variety of possible causes of CNS tumors, including viruses. Different types of CNS tumors occur in different age groups. For example, some types of CNS tumors are more common in children younger than three. Head injury does not appear to cause a CNS tumor.

A small number of CNS tumors occur in families. However, only a small percentage of children with a brain tumor have an identifiable genetic cause, usually in association with a familial disease called neurofibromatosis. Neurofibromatosis is an inherited disorder that causes neurofibromas (noncancerous tumors) to form on peripheral nerves in the body, brown spots on the skin, and deformities of tissues and bones. Neurofibromatosis is also called Recklinghausen's disease or von Recklinghausen's disease. Learn more about neurofibromatosis Type 1 and neurofibromatosis Type 2. Other, less common genetic conditions associated with a higher risk of a CNS tumor include Li-Fraumeni syndrome, tuberous sclerosis, nevoid basal cell syndrome, and Turcot syndrome.