Neurofibromatosis 1 (NF1) is an autosomal dominant disorder caused by genetic alterations of the NF1 gene on 17q11.2. About 30% of NF1 patients develop plexiform neurofibromas (PNFs), which often cause severe clinical deficits. To determine whether there is a certain genotype underlying PNFs or subtypes of PNFs, we screened 42 NF1 patients from 41 families with PNFs for mutations in the NF1 gene. In 33 out of the 41 (80%) unrelated patients NF1 mutations were found, 24 are novel while the other 9 have been described in previous studies. The 33 mutations included 23 nonsense and frameshift, six splice and four missense mutations. The tumors in these patients had various sizes and features/growth characteristics. No correlation was found between the type or location of the NF1 mutations and size, location or feature of the PNFs, suggesting that many types of NF1 mutations can lead to development of PNFs.