Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder characterised by cafè au lait spots, multiple neurofibromas and Lisch nodules of the iris, with marked variability of expression. The NF1 gene is located at 17q11.2, spans 350 kb genomic DNA and comprises 60 exons encoding a 11-13 kb transcript (Viskochil et al.). Four alternatively spliced NF1 transcripts have been identified and they show differential expression in various tissues. NF1 gene is a member of the tumor suppressor gene family. The protein encoded by NF1, neurofibromin, has a domain homologous to the GTPase activating protein (GAP) family, and downregulates ras activity. Neurofibromin is involved in the control of cellular growth and differentiation and germline mutation analysis has shown that around 82% of all the fully characterised NF1 specific mutations so far predict severe truncation of neurofibromin. The current demand for molecular diagnosis of NF1 is low. Many couples would probably request a prenatal diagnosis if it could predict disease severity. Molecular prediction of disease severity and prognosis may either be very complicated or even impossible. Presymptomatic DNA diagnosis is probably not going to be in huge demand because the clinical diagnosis of NF1 is usually straightforward, even in early childhood. Further knowledge of the gene function may also lead to the development of new therapy for the disease.