Meckel syndrome (MKS) is a lethal syndrome with a central nervous system malformation, usually occipital meningoencephalocele, bilaterally large multicystic kidneys with fibrotic changes of the liver, and polydactyly in most cases. Additional anomalies are frequent. A common characteristic of the parenchymal changes of many organs is a proliferation of the stromal connective tissue and increase and dilatation of the associated epithelial ducts. Autosomal recessive inheritance is well confirmed and the gene locus has been mapped to chromosome 17q21-24 by genome wide linkage study. The locus was later refined to within a less than 1 cM region (17q22), in which most of the Finnish MKS patients share a common chromosomal haplotype suggesting one major and relatively old mutation. However, in most of the non-Finnish MKS families studied, this linkage could not be confirmed. The linkage studies provide evidence that more than one locus is involved in bringing about the combination of CNS malformations, cystic kidneys, and polydactyly, maybe even in typical cases of MKS. Prenatal diagnosis of MKS by vaginal ultrasound scan is possible from 11-12 weeks of pregnancy, especially in families where there is a known risk. In those families where linkage to 17q22 is established, prenatal diagnosis by DNA analysis is possible.