Matrix metalloproteinase (MMP) 3 plays an important role in the pathogenesis of myocardial infarction (MI). Up to now, there has been conflicting data regarding the possible contribution of the MMP3 -1612 5A/6A promoter polymorphism to MI. In this study, we have investigated the possible association of three polymorphisms (-1612 5A/6A, -376C/G, Glu45Lys) in the MMP3 gene with MI in a Chinese Han population. The polymorphisms were analyzed in 509 patients with MI, and in 518 healthy controls. The frequency of the 5A allele was 14% in the healthy controls, which is less than in Western populations (40%-52%). Logistic regression analyses of individual polymorphisms indicated that individuals carrying the -1612 5A allele had an increased risk of MI (odds ratio [OR] 1.75, 95% confidence interval [CI] 1.28 to 2.40), as did those carrying the -376 G allele (OR 1.78, 95% CI 1.33 to 2.38). The three polymorphisms studied were found to be in strong linkage disequilibria. Haplotype analyses showed that the 5A-G-Lys haplotype (-1612 5A, -376G and 45Lys) was independently associated with susceptibility to MI. Taken together, the effect of the MMP3 polymorphisms studied may be attributable to the -1612 5A/6A polymorphism. We conclude that the MMP3 -1612 5A/6A polymorphism is associated with MI in our population, implying that individuals of the 5A allele carriers have an increased risk of suffering MI.