There exist a large variety of rare chromosomal disorders. Information about these disorders is not only difficult to obtain for patients and their relatives but for clinicians as well. Due to new techniques that enable geneticists to study the chromosomes immure detail the number of detectable chromosomal abnormalities will considerably raise over the coming years. We have started a European initiative to collect medical data on the various rare chromosomal abnormalities: the European Cytogeneticists Association Register of Unbalanced Chromosomal Aberrations (ECARUCA). One of the major goals of ECARUCA is to make the new data available to the clinicians and the patients/families involved. To achieve this we will be setting up a database that will be accessible to account holders through the Internet.