Only a few cases with breast cancer and neurofibromatosis type 1 (NF1) have been reported in the literature. Here, we present a family with a history of neurofibromatosis and breast cancer. No hereditary NF1 mutation was observed in this case. Loss of heterozygosity (LOH) analyses of the breast tumor revealed LOH in the NF1 region. In this family, the proband and her mother had breast cancer. The proband was diagnosed with breast cancer at the age of 23 years. No BRCA1 or BRCA2 mutations were observed in the proband's peripheral blood DNA nor were such mutations observed in the immunohistochemically analyzed paraffin block of the tumor DNA. Neurofibromin, encoded by the NF1 gene region, was reported as nearly absent in human breast cancer-MDA-MP-231 cells. Neurofibromin is similar in function to the GTPase activating protein (GAP), p120 GAP. It also accelerates the inactivation of the RAS oncogene. Molecular alterations in NF1 gene region cause neurofibromatosis. LOH in the tumor tissue of our case supports the role of the NF1 gene in the etiology of some cases of breast cancer.