AbstractWe report two cases of prenatal detection of lissencephaly by high‐resolution ultrasound. The first case studied was referred for high‐risk obstetrical management and serial antenatal ultrasounds because of a family history of lissencephaly in an unresolved chromosomal abnormality. Diagnosis of a smooth gyral pattern consistent with lissencephaly was made at 32 weeks' gestation. The second case was referred for prenatal ultrasound because of a size versus dates discrepancy. The ultrasound examination showed a smooth gyral pattern at 31.5 weeks. In light of this ultrasound finding, a fetal blood sample was obtained and a chromosomal abnormality reported, confirming the diagnosis. To our knowledge, these cases represent the first report of the sonographic prenatal diagnosis of cerebral agyria or lissencephaly.