A 7-year-old girl with neurofibromatosis type I (NF1) was diagnosed to have monosomy 7 myeloproliferative disease (Mo 7-MPD). Of the benign and malignant tumors that are encountered with increased incidence in NF1, those originating from the neural crest are frequent. However, tumors that do not originate from the neural crest may also be seen and among these, myeloid leukemias are prominent. Studies on NF1 patients with Mo 7-MPD and juvenile chronic myeloid leukemia (JCML) have suggested the role of the NF1 gene in the leukemogenesis. The relationship between monosomy 7 and hematological malignancies is already known. These finding are in agreement with the multistep development theory of cancer. In addition, our case is one of the very rare NF1 cases having father to daughter inheritance with a myeloid malignancy. We believe that cytogenetic and molecular genetic studies will contribute to further understanding of leukemogenesis.