The biology of AML is reflected through several prognostic factors. Until now there has been no general agreement about these factors. In most studies therapy is not stratified according to risk factors with the exception of age. Since 1976 the FAB classification has been the basis for the diagnosis in AML. But only for the AML M3 is this important for the choice of treatment. Therefore, it is unclear if the FAB classification is the best way to describe the individual biology in AML. We are able to verify that significant differences in remission rates and event-tree survival are much better reflected by the cytogenetic results. With data from the AML cooperative group on one hand and in a kind of meta-analysis with cytogenetic date from different studies on the other hand, we are able to conclude that cytogenetics are much more feasible to describe the biological entity in AML patients. Further studies should focus more on this individual prognostic factor.