This review summarizes the findings of genetic association studies on common diseases. The authors highlight that over 600 associations between common genetic variants and diseases have been reported, but most are not robust. Only six of 166 associations studied multiple times were consistently replicated. The authors discuss possible reasons for this irreproducibility, including population stratification, linkage disequilibrium, gene-gene and gene-environment interactions, and weak genetic effects. They emphasize the need for caution in interpreting single studies and suggest guidelines for conducting and interpreting genetic association studies. The review also presents two examples: the association between factor V Leiden and deep venous thrombosis, and the association between MTHFR polymorphisms and various diseases. The authors conclude that while genetic association studies have the potential to improve disease prevention, prediction, and treatment, their results must be carefully evaluated to avoid false positives. They stress the importance of replication and meta-analysis to determine the validity of genetic associations. The review also addresses ethical concerns related to genetic testing and the potential for misuse. Overall, the authors argue that while genetic association studies are valuable, their results must be interpreted with caution due to the high rate of irreproducibility.This review summarizes the findings of genetic association studies on common diseases. The authors highlight that over 600 associations between common genetic variants and diseases have been reported, but most are not robust. Only six of 166 associations studied multiple times were consistently replicated. The authors discuss possible reasons for this irreproducibility, including population stratification, linkage disequilibrium, gene-gene and gene-environment interactions, and weak genetic effects. They emphasize the need for caution in interpreting single studies and suggest guidelines for conducting and interpreting genetic association studies. The review also presents two examples: the association between factor V Leiden and deep venous thrombosis, and the association between MTHFR polymorphisms and various diseases. The authors conclude that while genetic association studies have the potential to improve disease prevention, prediction, and treatment, their results must be carefully evaluated to avoid false positives. They stress the importance of replication and meta-analysis to determine the validity of genetic associations. The review also addresses ethical concerns related to genetic testing and the potential for misuse. Overall, the authors argue that while genetic association studies are valuable, their results must be interpreted with caution due to the high rate of irreproducibility.