Williams syndrome (WS) is characterized by cardiac and vessel malformations as well as cognitive abnormalities. The syndrome is caused by a 1.5-1.6 Mb deletion in the long arm of chromosome 7. The genes in this region are largely known, but for some of them the function is not yet clarified. The objective of this study was to summarize knowledge about the correlation between genotype and phenotype for WS. WS can serve as a model for syndromes caused by micro deletions. Material and methods: A review of the literature, including both laboratory studies and clinical studies. The literature searches were conducted using the Pubmed interface for Medline. Results: The articles included were reviewed systematically. Correlation data were collected in tables. ELN, coding elastin, is responsible for the cardiac defects in WS. Mapping the cognitive abnormalities to specific genes has been more difficult. LIMK1, CLIP-115 and GTF2I are important candidate genes. Discussion: At present, one cannot clearly link genes and phenotype in WS. It is likely that other genes in the individual patient are important for the clinical phenotype, as well as effects from other genes within the deletion.