Genetic factors appear to be important in the restenotic process after percutaneous coronary intervention (PCI), as well as in inflammation, a pivotal factor in restenosis. TNFalpha, a key regulator of inflammatory responses, may exert critical influence on the development of restenosis after PCI. The GENetic DEterminants of Restenosis (GENDER) project included 3104 patients who underwent a successful PCI. Systematic genotyping for six polymorphisms in the TNFalpha gene was performed. The role of TNFalpha in restenosis was also assessed in ApoE*3-Leiden mice, TNFalpha knockout mice, and by local delivery of a TNFalpha biosynthesis inhibitor, thalidomide. The -238G-1031T haplotype of the TNFalpha gene increased clinical and angiographic risk of restenosis (P=0.02 and P=0.002, respectively). In a mouse model of reactive stenosis, arterial TNFalpha mRNA was significantly time-dependently up-regulated. Mice lacking TNFalpha or treated locally with thalidomide showed a reduction in reactive stenosis (P=0.01 and P=0.005, respectively). Clinical and preclinical data indicate that TNFalpha plays an important role in restenosis. Therefore, TNFalpha genotype may be used as a risk marker for restenosis and may contribute to individual patient screening prior to PCI in clinical practice. Inhibition of TNFalpha may be an anti-restenotic target strategy.