We evaluated the effects of platelet transfusions and intravenous immunoglobulin (IVIG) in neonates with fetal and neonatal alloimmune thrombocytopenia (FNAIT) with and without antenatal treatment with IVIG. Records of neonates with FNAIT admitted between January 2000 and November 2005 were reviewed. The patients were divided into group I, treated antenatally with IVIG for known FNAIT, and group II, postnatally diagnosed with FNAIT. The primary outcome was the time interval to reach a platelet level above 100 x 10(9)/L in relation to the type of treatment. Nineteen neonates with FNAIT were identified, 13 in group I and 6 in group II. In group I, four children were born with a platelet count above 100 x 10(9)/L and never needed treatment, and four received a single matched platelet transfusion at birth with a maintained response. Five neonates received IVIG and one matched transfusion, with all but one rapidly responding. In antenatally treated cases, postnatal IVIG had no apparent effect on the platelet count. In group II, two neonates died on day 1 with severe intracranial hemorrhage. Two of the four other patients responded to a number of unmatched platelet transfusions, with one neonate rapidly responding after one matched transfusion, while another needed nine matched transfusions before a persistent adequate platelet count was reached after 9 weeks. Postnatal IVIG had no apparent effect on the platelet count in any of our cases. In neonates with FNAIT treated antenatally with IVIG, neonatal management using a single matched platelet transfusion was adequate in all cases. In neonatally diagnosed cases not treated before birth, multiple matched platelet transfusions may be required. We found no evidence to support the use of IVIG in neonates with FNAIT.