The neurofibromatosis type 1 (von Recklinghausen, NF1) gene has been proposed as a suppressor gene in tumors associated with neurofibromatosis. Recent publications have indicated that the NF1 gene can be rearranged in neuroblastoma cell lines. We analyzed DNA from a neuroblastoma patient with NF1 inherited as a familial trait on the paternal side. Using PCR and Southern techniques we showed that the patient had a constitutional deletion of several exons of the paternally derived NF1 gene and that the maternal copy of the gene had been deleted in the tumor of the patient. This is the first instance of a homozygous deletion reported in a primary neuroblastoma tumor. This suggests that NF1 inactivation in involved in the development or progression of some neuroblastomas in agreement with the hypothesized two hit model of inactivation for a tumor suppressor. These results are concordant with other groups that have detected unbalanced translocations t(1;17) in neuroblastoma tumors, with a breakpoint in chromosome 17 that may coincide with the location of the NF1 gene.