Thrombocytopenia is a common hematologic disorder in the neonatal period. It can occur in neonates hospitalized in the Intensive Care Unit and in preterm infants. It is characterized by a platelet count of less than 150.000/mm3. In the context of immune thrombocytopenia, neonatal thrombocytopenia due to maternal alloimmunization (estimated at 1 per 1000 live births) is not a rare event but it is often undiagnosed in minor forms. This is caused by maternal immunization against fetal platelet antigens inherited from the father and lacking in the mother. Maternal IgG alloantibodies cross the placenta causing fetal platelet destruction. In severe thrombocytopenia, consequences can be severe, with intracranial bleeding occurring in 10-30% of patients. Diagnosis is essentially based on clinical examination and must be suspected by pediatricians.