Neurofibromatosis (NF) is a genetic disorder causing skin abnormalities and tumors that form on nerve tissues. These tumors can be small or large and can occur anywhere in the body, including the brain, spinal cord, large nerves, or smaller nerves. NF affects persons of both sexes and all racial groups. There are 2 types of neurofibromatosis, called NF1 and NF2. These are 2 distinct disorders that are caused by mutations (changes) in different genes. NF1 is also referred to as von Recklinghausen disease and is a rather common genetic disease, affecting approximately 1 in 3000 individuals. Some patients who have NF1 only display characteristic skin abnormalities such as café au lait spots , which are flat, hyperpigmented (darker than surrounding skin) areas. Other patients can have severe physical complications such as malignant (cancerous) tumors or have mental retardation. NF2 is much more rare than NF1, affecting less than 1 in 30 000 individuals, usually becoming apparent in the late teens, and typically causing hearing loss and problems with balance due to tumors on nerves to the ears. The November 18, 2009, issue of JAMA includes an article about a recently described condition called Legius syndrome in which patients have skin pigment abnormalities indistinguishable from NF1. This Patient Page is based on one published in the July 16, 2008, issue of JAMA.