Genetic factors are thought to contribute to the pathogenesis of acute myocardial infarction (AMI). A common variant of factor XIII (FXIII), FXIII Val34Leu, may be protective against developing an AMI, but various studies show conflicting results. We performed a meta-analysis to determine whether the FXIII Val34Leu variant is associated with a decreased risk of AMI. One hundred ninety-five articles were reviewed and 12 case-control studies were selected. We included studies involving patients with objectively diagnosed AMIs (WHO criteria), provided that FXIII Val34Leu genotyping data were available. Inclusion decisions, quality assessment, and data extraction were conducted by two reviewers. Hypothesizing that the Leu allele was protective, we performed three analyses with the Val/Val genotype as the reference group. Pooled odds ratios (OR) and their 95% confidence intervals (95% CI) were determined. Prior to pooling, heterogeneity testing was performed using the I(2) statistic. These studies included a total of 8,743 patients, of which 3,663 were AMI patients and 5,080 were healthy controls. Using the random effects methods, protective effects were seen with the Leu/Val genotype alone (OR 0.79, 95% CI 0.68-0.93) and with Leu/Val and Leu/Leu genotypes combined (OR 0.79, 95% CI 0.66-0.93). There was also a protective effect with the Leu/Leu genotype alone, (not statistically significant: OR 0.83, 95% CI 0.61-1.12), likely due to the low frequency of this genotype. These results suggest that there is an association between the factor XIII Leu allele and a modest protective effect against AMI and may provide useful information in profiling susceptibility to myocardial infarction.