Neurofibromatosis 1 is a progressive multisystem disorder. The hallmark feature is the occurrence of nerve sheath tumors, neurofibromas. Other features include tumors such as optic gliomas and malignant peripheral nerve sheath tumors. There are also nontumor manifestations, such as skeletal dysplasia and learning disabilities. Since the NF1 gene was identified, much has been learned about the molecular genetics of the disorder; recently, this has led to insights about pathogenesis. Ultimately, it is hoped that this will be translated into specific means of treatment. This review describes the various clinical features of neurofibromatosis 1 and considers them in the context of the pathophysiology of the disorder. (J Child Neurol 2002; 17:573-577).