Advances in DNA technology and the discovery of DNA polymorphisms have permitted the creation of DNA databases of individuals for the purpose of criminal investigation.Many ethical and legal problems arise in the preparation of a DNA database, and these problems are especially important when one analyses the legal regulations on the subject.In this paper three main groups of possibilities, three systems, are analysed in relation to databases. The first system is based on a general analysis of the population; the second (...) one is based on the taking of samples for a particular list of crimes, and a third is based only on the specific analysis of each case. The advantages and disadvantages of each system are compared and controversial issues are then examined. We found the second system to be the best choice for Spain and other European countries with a similar tradition when we weighed the rights of an individual against the public's interest in the prosecution of a crime. (shrink)