The von Willebrand factor (vWF) is a highly multimerized glycoprotein that promotes platelet adhesion and aggregation at a high shear rate, and also acts as a carrier of coagulation factor VIII. vWF has been identified as a risk factor for recurrent myocardial infarction in the general population. It has been reported that two polymorphisms of vWF gene promoter and the Thr789Ala polymorphism in vWF gene are associated with arterial thrombosis. The Sma I polymorphism is located in intron 2 of vWF gene. The relevance of this polymorphism to thrombotic disease was investigated by genotypic identification in two case-control studies: 107 patients with acute ischemic stroke, 49 patients with acute myocardial infarction (AMI), and 113 health controls age- and race-matched for each patient. Twenty-eight (26.2%) of the 107 patients with acute ischemic stroke, 8 (16.3%) of 49 patients with AMI, and 11 (9.7%) of 113 controls were found to be homozygous for CC genotype, respectively. The prevalence of the CC genotype in acute ischemic stroke was significantly higher than that of the normal controls (odds ratio [OR]=3.29, 95% confidence interval [CI]=1.54-7.01,.01>P>.001). However, the prevalence of the CC genotype in AMI was not significantly different from that of the normal controls (OR=1.81, 95% CI=0.68-4.82,.30>P>.20). Plasma vWF:Ag was also determined by enzyme-linked immunosorbent assay (ELISA) on the frozen plasma of 122 subjects. The mean plasma vWF:Ag levels of the controls, patients with acute ischemic stroke, and AMI were 0.468, 0.584, and 0.783 U/ml, respectively. The mean level of plasma vWF:Ag did not differ significantly between controls and patients with acute ischemic stroke (P=.195), but had significantly difference between controls and patients with AMI (P=.001). No association was found between the Sma I polymorphism and vWF plasma levels in controls, patients with acute ischemic stroke, or the AMI group (one-way ANOVA, P=.323, P=.315, P=.96). Results show that the Sma I polymorphism is strongly associated with increased risk of acute ischemic stroke, however, no association was observed between this polymorphism and AMI. This polymorphism of vWF may represent a newly identified risk factor for acute ischemic stroke in Chinese. Whether it is the real functional variant associated with acute ischemic stroke remains to be elucidated.