The term idiopathic neutropenia describes various types of neutropenia that may occur at any point in life for unknown reasons. As already described for the other types of neutropenia, frequency and severity of infections is correlated with the neutrophil counts. Neutrophil counts and clinical problems in these patients vary considerably, but in general the more severe the neutropenia the more serious and frequent the infections. Most patients respond well to G-CSF treatment but require long term treatment. There is no evidence for any increased risk of MDS or leukemia in patients with idiopathic neutropenia, whether or not they receive G-CSF therapy. Likely the causes of idiopathic neutropenia are multifactorial and may include autoimmune, genetic and physiologic causes.