Many of the neurocutaneous disorders are more common than once suspected, in part because patients with milder forms of the disorders are now more likely to be recognized. Improved diagnostic studies and increasingly specific medical and surgical therapy allow some previously untreatable complications to be successfully managed. Genetic linkage analysis has localized the abnormal gene for some of the hereditary neurocutaneous disorders onto specific chromosomes, and newly developed clinical diagnostic criteria have improved our ability to establish a definite diagnosis in less obvious patients. Thus, the outlook for these patients is no longer uniformly pessimistic.