Three infants presented with the onset of hemifacial spasm after birth and at the age of 10 months. One patient was found to have occlusion of the straight sinus and large collateral veins at the base of the brain, presumably due to venous sinus thrombosis, supporting the concept of vascular compression of the facial nerve at its exit from the brain stem as a mechanism for the production of hemifacial spasm. The other patients each had an intrinsic mass compressing the fourth ventricle, located in the lower pons and extending into the cerebellar vermis and right cerebellar peduncle in one; in the other patient, the mass involved the cerebellar vermis and right middle cerebellar peduncle alone. These patients widen the etiologic spectrum of the syndrome and show that serious intracranial diseases may underlie hemifacial spasm in infancy.