Objectives: Intracranial atherosclerosis, especially the middle cerebral artery (MCA), is the commonestvascular lesion for ischemic stroke the Chinese population. We explored the association of geneticpolymorphism and environmental factors in MCA atherosclerosis in the Chinese population. Methods:One hundred fifty-six ischemic stroke patients with MCA stenosis and 181 well-matched ischemicstroke patients without MCA stenosis were examined by polymerase chain reaction (PCR). ThePCR products were analyzed for lipoprotein lipase (LPL) S447X and paraoxonase1 (PON1) Q192Rpolymorphisms by restriction enzyme digestion. Medical history documentation and investigationof biochemical markers were performed for each subject. Results: Univariate analysis showed thatthe levels of systolic blood pressure (SBP) were higher in the MCA stenosis group. There were nosignificant differences in the genotype and allele frequencies of the LPL S447X and PON1 Q192Rpolymorphism observed between the two groups. But, in the patients above 60 years of age with andwithout MCA stenosis, LPL X carriers have higher level of SBP than the LPL SS genotype carriers.Multivariate logistic regression found that SBP was the significant, independent predictor of thepresence of MCA stenosis patients above 60 years of age (P < 0.001, OR=1.206, 95% confidenceintervals: 1.014-1.032).Conclusions: SBP appears to contribute to the pathogenesis of MCA stenosis among Chinese. Thegene polymorphism of LPL S447X may be associated with atherosclerotic MCA stenosis in Chinesepopulation.