Fanconi's anemia (FA) is a congenital bone marrow failure syndrome with a high risk of developing hematological malignancies. Hematopoietic growth factors have been shown to improve the hematological status in FA patients. We studied the efficacy of G-CSF in four FA patients with severe neutropenia and no evidence of cytogenetic abnormalities. Three patients were given 3 courses of G-CSF: the first at a dose of 5 μg/kg/day for two weeks, the 2nd at 5μg/kg every second day for two months, followed by a maintenence therapy with G-CSF twice a week. All patients had an increase in their absolute neutrophil count, which lasted as long as the therapy was continued. Neither improvement in platelet count and hemoglobin concentration nor effect on transfusion requirements were seen. CFU-GM and BFU-E were undetectable before, during and after treatment. The reduction in number and severity of infections resulted in a marked improvement of clinical status. In the fourth patient G-CSF treatment was stopped after 4 weeks because of the rise of WBC over 30.000/uL with immature myeloid cells. Cytogenetic analysis revealed monosomy 7. The patient died of complications after receiving haploidentical maternal bone marrow. During maintenance one patient showed immature cells in peripheral blood and stopped G-CSF treatment; two months later the patient died because of infections. A second patient received G-CSF for 18 months, then was transplanted from an unrelated donor. The third patient has been on G-CSF therapy since 48 months and keeps in good clinical condition. In conclusion, G-CSF is an effective treatment for severe neutropenia with recurrent infections in FA. We observed a myelodisplastic syndrome in 2/4 G-CSF-treated patients; thus a close monitoring is needed during G-CSF administration.