Fetal/neonatal alloimmune thrombocytopenia (NAIT) results from fetomaternal mismatch for human platelet alloantigens leading to antibody-mediated destruction of fetal platelets. This is one of the most common causes of severe thrombocytopenia in the newborn with an incidence of 1/800-1,000. In the most severe cases, NAIT may result in intracranial hemorrhage and may lead to death or neurologic sequelae. We report a case of fetal hydrocephalus caused by NAIT and discuss the importance of making an accurate prenatal diagnosis to improve the management of the current pregnancy and the outcome of subsequent pregnancies. Screening of female siblings of affected cases is recommended in order to detect at-risk individuals.