RESUMO
Etiological diagnosis is a very important aspect in neonatal neutropenias because of different prognosis that implies. Isoimmune neonatal neutropenia is one of these processes, with good prognosis and which is rarely diagnosed; it is due to maternal isoimmunization during pregnancy against a foetus specific neutrophil antigen, inherited from the father. Authors present a case, in which a deep neutropenia during the first fifteen days of life, was observed with high monocytosis and without other associations; baby returned to normal levels when he was three months old. Presence of an antineutrophil antibody in mother's serum, with specificity against father's and baby's granulocytes was demonstrated. Bibliography is revised and differential diagnosis and treatment is discussed.
