Genome-wide association studies (GWAS) are aimed to identify genetic markers of complex human diseases and individual traits. In this context more than 150 gene loci have been found to be associated with about 60 different diseases and personal characteristics. A recent example is the relevance of a polymorphism in the interleukin 28B gene for the natural course of hepatitis C virus infection and the efficacy of antiviral therapy. It is to be expected that GWAS will increasingly contribute to the understanding of the pathogenesis and consquently improve prediction, prevention, diagnosis and therapy of human diseases and eventually will become part of clinical practice.