After the successful sequencing of the human genome the genetic variation between individuals will be worked out in the near future. The genetic differences are the basis for different predispositions to diseases. The next goal is to correlate the host of genetic variants with phenotypes. This endeavor has already been successful for monogenic diseases; however, it will also be possible in genetically complex diseases. If a trait follows a monogenic mode of inheritance, a phenotype results nearly completely from a single mutation; in genetically complex diseases there exists only a statistical relationship. Predictive genetic diagnostics should only be considered after genetic counseling; it makes sense, if there exists efficient prevention or therapy, respectively. This applies e. g. to various familial cancer predispositions. In the future, medical doctors should be able to apply genetic risk figures and to convey them to their patients.