Alloimmunization to granulocyte-specific antigens can occur during pregnancy. Maternal antibodies of IgG class can cross the placenta to result in alloimmune neonatal neutropenia. Antibodies to human neutrophil antigens anti-HNA-1a, HNA-1b, and HNA-2a have been most commonly reported to cause alloimmune neonatal neutropenia. Isoantibodies to Fc gamma RIIIb (CD16) if mother is a HNA-null phenotype are rarely involved in neonatal neutropenia. We report on a case of severe neutropenia (440 neutrophils/muL) due to anti-Fc gamma RIIIb (CD16) isoimmunization. On day 14 severe omphalitis developed, which was treated for 7 days by an antibiotic (ceftriaxone in a dose of 80 mg/kg/d) according to umbilical swab finding. Omphalitis persisted for 10 days in spite of antibiotic therapy and only resolved upon the introduction of rhG-CSF therapy. Therapy with rh-GCSF proved efficient and led to neutrophil count increase to 1970/muL and cure of omphalitis. However, therapeutic effect on granulocyte count was of transient nature, as granulocyte count fell to 760 n/muL on day 4 of therapy discontinuation. Neutropenia persisted for 2 months. The newborn was discharged from the hospital on day 26 with normal clinical status with clinical and laboratory control examinations at 2-week intervals. No additional infections were observed during the course of neutropenia.