In WEXPZ-En-1 transgenic mice, Engrailed-1, a homeodomain-containing transcription factor, is ectopically expressed in the embryonic midbrain and hindbrain under control of the Wnt-1 enhancer. En-1 is a development regulatory control gene which has an essential role in the formation of the midbrain and cerebellum. Approximately 28% of WEXPZ-En-1+ mice develop hypoplasia of the cerebellar vermis, 4th ventricular dilatation, cerebellar cyst and postnatal hydrocephalus, thus comprising key features of the Dandy-Walker malformation in humans. This mouse strain may therefore serve as an animal model for Dandy-Walker malformation, and raises the possibility that abnormal regulation of ENGRAILED genes, or targets of ENGRAILED, may be involved in the pathogenesis of this clinical condition.