Neutropenia, defined as an absolute neutrophil count (ANC) <1.5 × 10(9)/L, encompasses a wide range of diagnoses, from normal variants to life-threatening acquired and congenital disorders. This review addresses the diagnosis and management of isolated neutropenia, not multiple cytopenias due to splenomegaly, bone marrow replacement, or myelosuppression by chemotherapy or radiation. Laboratory evaluation generally includes repeat complete blood cell counts (CBCs) with differentials and bone marrow examination with cytogenetics. Neutrophil antibody testing may be useful but only in the context of clinical and bone marrow findings. The discovery of genes responsible for congenital neutropenias now permits genetic diagnosis in many cases. Management of severe chronic neutropenia includes commonsense precautions to avoid infection, aggressive treatment of bacterial or fungal infections, and administration of granulocyte colony-stimulating factor (G-CSF). Patients with severe chronic neutropenia, particularly those who respond poorly to G-CSF, have a risk of eventually developing myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML) and require monitoring for this complication, which also can occur without G-CSF therapy. Patients with cyclic, idiopathic, and autoimmune neutropenia have virtually no risk of evolving to MDS or AML. Hematopoietic stem cell transplantation is a curative therapy for congenital neutropenia with MDS/AML or with cytogenetic abnormalities indicating impending conversion.