There are several forms of congenital neutropenia varying in the severity of reduction of neutrophil counts and the associated clinical problems. In one severe form, congenital agranulocytosis or Kostmann’s syndrome, neutrophils are severely reduced from birth, often to less than 0.1 x 109 /L. There is often a mild increase in blood monocytes and blood and marrow eosinophils, but the reasons for this observation are not known. The increase may be due to higher levels of endogenous haematopoietic growth factors during chronic inflammation, or because production of blood cells is diverted away from the neutrophil lineae. Neutrophil counts are always quie low, but in some patients, in response to severe illness and infection, slightly higher counts may be observed. Many of these patients have chronic infections with secondary anemia and elevated platelet counts. When severe hypoproliferative anemia or significant thrombocytopenia are seen in neonates and very young children, other diagnoses such as congenital aplastic anemia should be considered. In other patients with congenital neutropenia, still with counts usually less than 0.5 x 109 /L. Data from large series of cases indicate that there are indistinct boundaries between patients who might be classified as having Kostmann’s syndrome or congenital agranulocytosis, and those regarded as having more benign forms of congenital neutropenia.