Neutrophils have an important role in host defense and acute inflammation. It is well known that susceptibility to infection increases when the neutrophil count is low. Neutropenia were classified as mild, moderate and severe according to the neutrophil counts, or acute and chronic depending on the duration of neutropenia, or congenital and acquired according to the mechanism. The patients with neutropenia are clinically different due to underlying mechanism, they have life-threatening infections or no infection may be observed. The most common cause of acquired neutropenia is viral infection, followed by drugs and autoimmune neutropenia. Congenital neutropenia are usually diagnosed by acute and life-threatening invasive bacterial and fungal infections. Immune system disorders and other systemic abnormalities may be accompanied or not. Recent years, novel single gen defects causing congenital neutropenia were defined through advanced genetic techniques. Molecular diagnosis is useful for risk stratification, choice of therapy and prognosis on follow-up. This review was prepared for pediatricians as a guide focused on approach neutropenia, which tests should be performed and when should be referred to a specialist.