A partial or complete defect of the cerebellar vermis may occur sporadically or as a component of the Dandy-Walker syndrome, the Dandy-Walker variant, Down's syndrome, or Joubert-syndrome. We identified a defect of the cerebellar vermis in nine fetuses on routine antenatal sonographic studies. In five of the nine fetuses other abnormalities, including central nervous system and non-central nervous system lesions were identified. Three of these five fetuses died and two infants have remained well on follow-up. Four of nine fetuses (or infants) had no other abnormalities and have remained well on follow-up at 8 weeks to 4 years of age. Although cases of fatal and serious nonfatal outcomes have been reported by other investigators, in this small series the finding of an isolated inferior vermian defect was associated with a good prognosis.