Objective: To characterize the neuropathology of hereditary congenital facial palsy. Methods: The authors compared brainstem pathology of three members of one family with autosomal dominant congenital facial palsy to that in three age-ma tched controls. The neuropathologic findings of the familial patients were compa red with those of patients with Mbius syndrome.Results: The authors observed a marked decrease in the number of neurons in the facial motor nucleus with corre sponding small facial nerve remnants. In the patients with congenital facial pal sy the number of facial motoneurons ranged between 280 and 1,680 as compared to 5,030 and 8,700 for controls. No signs of neuronal degeneration or necrosis with neuronal loss,gliosis, or calcifications were present. There were no other abno rmalities of the rhombencephalon and its associated structures.The corticospinal tracts were fully developed. In contrast,Mbius syndrome is part of a more com plex congenital anomaly of the posterior fossa with hypoplasia of the entire bra instem,including the traversing long tracts, with signs of neuronal degeneration and other congenital brain abnormalities. Conclusion:Neuropathologic findings c onfirm clinical observations that hereditary congenital facial palsy and Mbius syndrome are two different entities with a different pathogenesis. Objective: To characterize the neuropathology of hereditary congenital facial palsy. Methods: The authors compared brainstem pathology of three members of one family with autosomal dominant congenital facial palsy to that in three age-ma tched controls. The neuropathologic findings of the familial patients were compa red with those of patients with Mbius syndrome. Results: The authors observed a marked decrease in the number of neurons in the facial motor nucleus with corre sponding small facial nerve remnants. In the patients with congenital facial pal sy the number of facial motoneurons ranged between 280 and 1,680 as compared to 5,030 and 8,700 for controls. No signs of neuronal degeneration or necrosis with neuronal loss, gliosis, or calcifications were present. There were no other abno rmalities of the rhombencephalon and its associated structures. the corticospinal tracts were fully developed. In contrast, Mbius syndrome is part of a more com plex congenital anomaly of the post erior fossa with hypoplasia of the entire bra instem, including the traversing long tracts, with signs of neuronal degeneration and other congenital brain abnormalities. Conclusion: Neuropathologic findings c onfirm clinical observations that hereditary congenital facial palsy and Mbius syndrome are two different entities with a different pathogenesis.