Miller-Dieker lissencephaly syndrome (MDS) is a human developmental brain malformation caused by neuronal migration defects resulting in abnormal layering of the cerebral cortex. LIS1, the gene defective in MDS, encodes a subunit of brain platelet-activating factor (PAF) acetylhydrolase which inactivates PAF, a neuroregulatory molecule. We have isolated murine cDNAs homologous to human LIS1 and mapped these to three different chromosomal loci (Lis1, Lis3, Lis4). The predicted sequences of murine Lis1 protein and its human homolog LIS1 are virtually identical. In the developing mouse and human, Lis1 and LIS1 genes were strongly expressed in the cortical plate. In the adult mouse Lis1 transcripts were abundant in cortex and hippocampus. The direct correlation between cortical defects in MDS patients and Lis1 expression in the murine cortex suggest that the mouse is a model system suitable to study the mechanistic basis of this intriguing genetic disease.