The term congenital neutropenia (CN) has been used for a group of hematological disorders characterized by severe neutropenia with absolute neutrophil counts (ANC) below 0.5)/109 L (1 associated with increased susceptibility to bacterial infections. This group of diseases includes primary bone marrow failure syndromes with isolated neutropenias like Kostmann syndrome and cyclic neutropenia, and neutropenias associated with metabolic or immunological disorders, like glycogen storage disease type 1b and Hyper IgM-syndrome, and neutropenias being one feature of a complex syndrome, like Shwachman-Diamond syndrome or Barth syndrome. To avoid confusion, we prefer using the term CN only for the most severe disorder among this group. Severe neutropenia characterized by an early stage maturation arrest of myelopoiesis leading to bacterial infections from early infancy. This disease has originally been described as Kostmann syndrome [14, 15] with an autosomal recessive inheritance. Recent pathogenetic investigations have demonstrated that this clinical phenotype includes different disorders, with a heterogenous pattern of inheritance including autosomal recessive, autosomal dominant and sporadic cases. Different point mutations in the neutrophil elastase gene have been detected in a subgroup of patients. Data on over 400 patients with CN collected by the Severe Chronic Neutropenia International Registry demonstrate that independent from the CN-subtype more than 90% of these patients respond to recombinant human granulocyte-colony stimulating factor (rHuG-CSF) with ANCs that can be maintained around 1.0)/109 L (1. Adverse events include mild splenomegaly, moderate thrombocytopenia, osteoporosis and malignant transformation into MDS/leukemia. Development of additional genetic aberrations, eg, G-CSF-receptor gene mutations, monosomy 7 or ras mutations during the course of the disease indicate an underlying genetic instability leading to an increased risk of malignant transformation. If and how rHuG-CSF treatment impacts on these adverse events remains unclear since there are no historical controls for comparison. Hematopoietic stem cell transplantation is still the only available treatment for patients refractory to rHuG-CSF treatment.