Severe congenital neutropenia is one of primary immunodeficiency disorders that characterized by severe neutropenia and is associated with severe systemic bacterial infections from early infancy. Granulocyte colony stimulating factor (GCSF) is clinically used as a treatment for congenital and acquired neutropenia. The aim of this study was evaluation of GCSF (PD- Grastim) in treatment of these patients. Patients with severe congenital neutropenia referred to Immunology, Asthma and Allergy Research Institute between Jan 2007 and Dec 2010 enrolled the study. Other causes of neutropenia were excluded by serial CBC and bone marrow studies, medical and drug histories and immunological tests. Patients were visited and examined monthly to evaluate their CBC and ANC (absolute neutrophil count), GCSF side effects and dosage adjustment. Cytogenetic studies were being done for all the patients for early detection of progression to AML/MDS. From twenty two patients who enrolled this study, 16 patients regularly evaluated. They were ten males and six females, range in age from 2 to 18 years old. Two patients failed to continue our follow up unfortunately and four patients died due to disease complications. Patients were followed for 24 to 48 months. In a period of 12-24 months before treatment, the mean of hospitalization frequency was 3.1 times and duration was 10 days; while during receiving treatment, they decreased to 0.2 times and 3 days, respectively (p<0.01). Also significant increase in mean ANC was observed during follow up (315/µl before treatment versus 1749/µl after 12 month regular treatment). Bone pain was the most common side effect. There have been no evidences of developing AML/MDS up to present time. Treatment with GCSF significantly reduced the duration and the frequency of hospitalization. Because of plausible progression to AML/MDS, regular follow-up of patients should be continued.