Hydrolethalus syndrome is a rare autosomal recessive (AR) disorder characterized by polyhydramnios, CNS abnormalities, cleft lip/palate, micrognathia, and polydactyly. Its molecular basis is unknown and prenatal diagnosis is challenging due to phenotypic overlap with several other midline malformation syndromes. A 34-year-old G3P2, nonconsanguinous, married, African-American woman was referred at 19 weeks of gestation after ultrasound findings of "multiple congenital anomalies." A previous pregnancy had been terminated following ultrasound findings of polyhydramnios, cleft lip/palate, polydactyly, severe hydrocephalus, and a Dandy-Walker malformation (DWM). Level II ultrasound evaluation of the current pregnancy demonstrated all of the anomalies which had been present in her previous pregnancy. Karyotype of amniocytes was 46,XX. Autopsy following pregnancy termination confirmed ultrasound findings. The pedigree, sonographic, and autopsy findings in this case were most consistent with hydrolethalus syndrome, although other AR multiple midline malformation syndromes were considered. Our case was detected by 19 weeks. Confident differential diagnosis is difficult for the geneticist and even more so for the sonologist given the technical limitations of ultrasound. It is uncertain whether these mendelian midline malformation syndromes represent slightly different phenotypic expressions of a common genetic defect or are manifestations of allelic and or locus heterogeneity. We suggest that for prenatal diagnostic purposes, in the absence of knowledge of the molecular basis of these disorders, the fine distinctions are not crucial as long as their mendelian inheritance is recognized and presence or absence of manifestations which make them severe are ascertained.