Study of Plexiform Neurofibromas in Neurofibromatosis Type 1

* INCLUSION * Diagnosis of Neurofibromatosis: All study subjects will fulfill two or more of the diagnostic criteria listed below for NF1. * Six or more caf(SqrRoot)(Copyright)-au-lait macules * 1.5cm or larger in postpubertal individuals * 0.5 cm or larger in prepubertal individuals * Two or more neurofibromas of any type or 1 or more plexiform neurofibroma * Freckling in the axilla or groin * Optic glioma (tumor of the optic pathway) * Two or more Lisch nodules (benign iris hamartomas) * A distinctive bony lesion * Dysplasia of the sphenoid bone * Dysplasia or thinning of long bone cortex * A first degree relative with NF-1 * Plexiform Neurofibroma: A plexiform neurofibroma fulfilling entry criteria for the study will be defined as a diffuse soft tissue or nerve enlargement in a patient with NF1 that is causing, or has potential to cause, disfigurement or functional disability. * Distribution of Plexiform Neurofibromas by site: A total of 300 plexiform neurofibromas will be studied, consisting of 100 tumors in the following three groups (based on region of maximal involvement): * Head and Neck * Trunk and Limbs (externally visible) * Trunk and Limbs (internal) \[spinal plexiform neurofibromas involve two or more levels with connection between the levels or extending laterally along the nerve\] * Subject Ascertainment: Study subjects will be ascertained at any of the participating clinical centers. It is expected that these will include subjects already followed in these clinics, as well as newly diagnosed patients EXCLUSION * Presence of metallic implant(s) that will make the patient unable to have MRI studies * Presence of medical or psychological condition that will make the patient unable to tolerate MRI studies or anesthesia (if needed) * Inability to image tumor or define tumor margins by MRI (which may be determined after the initial study) * Failure to obtain initial MRI within 60 days of enrollment * Previous radiation therapy to site of plexiform neurofibroma * Surgery involving the plexiform neurofibroma (excluding biopsy) within a six month period before enrollment * Current antineoplastic therapy * Entry of more than one member of the same family into the study is not permitted