It is important to determine whether the disorder was inherited or the result of a spontaneous mutation. At present, the best way to do this is through a thorough examination of each parent, including a skin examination and an eye examination looking for Lisch nodules. If neither parent is found to have signs of NF1, the child's disorder is most likely the result of a spontaneous mutation. When this is the case, parents often wonder if they did something to cause the mutation, perhaps exposing their child to radiation, medications, alcohol, or other things in the environment. The cause of the NF1 gene mutation is unknown; no environmental exposure has been implicated. It is important to remember that genetic mutations are not uncommon. Cells in the body are constantly dividing, and each time they do, an enormous volume of genetic information must be copied correctly. Random errors inevitably occur in the copying process and may be the "cause" of mutations leading to NF1. Further study of the NF1 gene is needed to know for certain.

Regardless of whether a person with NF1 inherited the disorder or developed it through a spontaneous mutation, all people with NF1 have a 50% chance of passing the disorder to a child. There is no way to predict the severity of the disorder in offspring; severely affected parents may have mildly affected children and vice versa. Scientists are currently developing genetic testing ("DNA testing") that may permit prenatal diagnosis for NF1. A physician or genetic counselor can provide additional information about the availability of such testing.