Severe neonatal thrombocytopenia is associated with a significant risk of neonatal bleeding complications. It may result from increased consumption, increased destruction, deficient production, or abnormal sequestration within the spleen. When immune mediated, most cases of clinically significant neonatal thrombocytopenia are due to maternal alloimmunization to paternally derived platelet antigens present on fetal platelets. We present the clinical, placental, and immunohematologic findings of a case of severe neonatal alloimmune thrombocytopenia (NAITP) complicated by additional HLA group alloimmunization. The placenta showed chronic villitis of unknown etiology (VUE) and diffuse microthrombi within the villous capillaries, indicating that abnormal thrombogenesis can be a complication of severe NAITP.