Neurofibromatosis is a rare genetic disorder that causes typically benign tumors of the nerves and growths in other parts of the body. Some people with this disorder have barely noticeable neurological problems, while others are affected profoundly. There are two major types: neurofibromatosis type I (NF1) and neurofibromatosis type II (NF2).

NF1 manifests itself at birth or during early childhood. NF1 is characterized by multiple light brown (café-au-lait) spots concentrated in the groin and underarms and benign tumors under the skin. Enlargement and deformity of bones and curvature of the spine (scoliosis) may also be present. On occasion, people with NF1 may develop tumors in the brain, on the cranial nerves or involving the spinal cord.

NF2 may appear during childhood, adolescence or early adulthood. NF2 is primarily characterized by benign tumors of the nerves that transmit sound impulses and balance signals from the inner ears to the brain. Tumors commonly affect both the left and right ("bilateral") auditory (hearing) nerves.

A third, related, disorder, called schwannomatosis, has been recognized. While schwannomatosis may share many features with NF1 and NF2, current evidence suggests that it is a distinct genetic disease. This disorder is more frequently diagnosed in adults aged 30 and older.