Neonatal alloimmune thrombocytopenia (NAIT) is due to an immune-mediated maternal-fetal platelet antigen incompatibility. Central nervous system abnormalities have been reported in infants with NAIT and include intracranial hemorrhage, ventriculomegaly, porencephalic cysts, neuronal migrational disorders, and, rarely, cerebellar lesions. We present the clinical and neuropathological findings from a case of a 3-day-old diamniotic/dichorionic female twin with known bilateral ventriculomegaly born prematurely at 33-1/7 weeks in gestational age. The pregnancy was further complicated by discordant intrauterine growth, intraventricular hemorrhage in the co-twin, and NAIT. At birth, the infant was noted to have diffuse body ecchymoses and petechiae and arthrogryposis. She subsequently developed multisystem organ failure and disseminated intravascular coagulopathy and died on the 3rd day of life. Neuropathological findings at autopsy included a posterior fossa cyst with no gross anatomic evidence of a cerebellum, atrophic pons and medulla with prominent pyramidal tracts and absent olivary nuclei, thinned corpus callosum, and symmetrical dilation of bilateral lateral ventricles. Microscopic examination confirmed the gross findings and revealed no histological evidence of cerebellar tissue, absence of superior and inferior cerebellar peduncles, and acute and chronic germinal matrix hemorrhages. Immunohistochemical studies revealed a focus of reactive gliosis at the base of the posterior fossa cyst with no evidence of cerebellar Purkinje or granule cells. To our knowledge, this is the 1st report with well-characterized neuropathological examination detailing complete cerebellar loss and brain-stem atrophy in a neonate with NAIT.