Neurofibromatosis is one of the most frequent autosomal-dominant hereditary disorders. Neoplastic, dysplastic and dysraphic lesions characterize the disease from the viewpoint of a neurologist. Depression, suicide, emotional instability, learning disability and behavior disorder are important aspects for the neuropsychiatric evaluation. Treatment of the patients will be facilitated by following the diagnostic criteria and by an interdisciplinary approach to diagnosis. The gene-molecular differentiation of NF I and NF II provides a basis for a more profound understanding of the disease which allows for more than just the clinical description. Cloning of the gene of NF I will give the possibility of predictive diagnosis of NF I. At present an indirect prenatal diagnosis of the genetic disorder is possible by flanking markers of NF I.