Neurofibromas are benign neoplasms of the peripheral nerve sheath, which appear everywhere on the body of almost every NF1 patient. Neurofibromas are composed of different cell types like Schwann cells, fibroblasts, mast cells and perineurial cells. If in Schwann cells of NF1 patients the wild-type NF1 allele is inactivated in a heterozygous microenvironment, a neurofibroma will be formed. There are 3 types of neurofibromas: cutaneous, subcutaneous and plexiform. Cutaneous and subcutaneous neurofibromas appear during adolescence as isolated nodules in or under the skin, respectively. Plexiform neurofibromas are congenital and can spread along a large segment of a peripheral nerve. NF1 microdeletion patients have in general more neurofibromas and they appear at a younger age.