Neonatal alloimmune thrombocytopenia (NAIT) is the most common cause of severe thrombocytopenia in term newborns. The cause of NAIT is feto-maternal incompatibility for platelet antigens inherited from the father. The most common antigen involved in the pathogenesis is HPA-1a (HPA, human platelet antigen). HPA-1a positive fetal thrombocytes cause maternal alloimmunization. Transplacental transfer of anti-HPA-1a antibodies into the fetal circulation leads to thrombocytopenia. The estimated incidence of NAIT is 1-2/1000-5000 live births. The frequency of alloimmunisation during the first incompatible pregnancy is 20-59%. The most common manifestation is bleeding into the skin, which may be the only clinical sign. The most severe repercussion of NAIT is intracranial hemorrhage (ICH) which can lead to neurodevelopmental disabilities. In cases of ICH, there is an increased recurrence rate of ICH in the subsequent pregnancies. NAIT should also be considered if neonatal thrombocytopenia is discovered incidentally. After clinical diagnosis is suggested, laboratory testing should be done in order to confirm the diagnosis of NAIT. For this purpose, serological testing and HPA genotyping is done. Therapy of the newborn with thrombocytopenia is based on transfusions of thrombocyte concentrates. Prenatal therapy is needed in women with a previously affected child. Intravenous immunoglobulins along with corticosteroids are the therapy of choice.