The diagnostic criteria and complications of neurofibromatosis (Von Recklinghausen's neurofibromatosis or peripheral neurofibromatosis) are summarized. Patients and their relatives were studied in pediatric departments of the University Hospitals at Amsterdam (n = 23) and Rotterdam (n = 39) using a multidisciplinary approach and a standardized protocol. This comprehensive evaluation enables improved detection of serious complications and their management, and information to the parents about this highly variable disorder. Also, more insight is obtained into the natural history of the disease. Genetic counseling and family studies will become more precise in the near future, now the gene for NF I has been localised on chromosome 17, and for NF II (central NF) on chromosome 22, enabling DNA-marker studies.