Neurofibromatosis (nu-ro-fi-bro-ma-tóe-sis), or NF, is a little-known disease that primarily affects the growth of neural (nerve) cells. This causes tumors to grow on nerves and produce other abnormalities such as skin changes and deformities. But NF may affect almost any organ of the body. It occurs equally in both men and women, in all races and ethnic groups. Because the symptoms are varied, uncertain, and progressive, NF is hard to define or picture.