Three multisite clinical trials have examined the efficacy of CYP2C9 plus VKORC1 genotype-guided warfarin, of which two trials demonstrated favorable effects of a genotype-guided approach on the outcome of improved anticoagulation control or reduction in risk for bleeding, thromboembolism, death, or supratherapeutic anticoagulation following total joint arthroplasty. This evidence concerns the gene VKORC1 and Thromboembolism.