Neurofibromatosis Type 1 (NF1) is a common genetic disease with an incidence of 1 in 3,000 to 4,000. Clinical manifestations may include cafe-au-lait macules, axillary freckling, neurofibromas, Lisch nodules, skeletal dysplasias, learning disabilities, and a variety of neoplasms. In persons with NF1, some malignancies occur at an increased incidence compared to the general population. These include central nervous system astrocytomas, especially involving the visual pathways; ependymomas; meningiomas; neurofibrosarcomas; rhabdomyosarcomas; nonlymphocytic leukemias; and pheochromocytomas. The authors discuss the dysplastic and malignant features associated with NF and the concept of NF as a "neurocristopathy."