Several studies have recently focused on the association between heme oxygenase-1 (HMOX1) gene promoter polymorphisms and susceptibility to type 2 diabetes mellitus; however, results have been conflicting. This systematic Human Genome Epidemiology review and meta-analysis was undertaken to integrate previous findings and summarize the effect size of the association of HMOX1 gene promoter polymorphisms with susceptibility to type 2 diabetes. The authors retrieved all studies matched to search terms from the PubMed/MEDLINE, EMBASE, and ISI Web of Science databases that had been published through December 31, 2009. The articles were then checked independently by 2 investigators according to the eligibility and exclusion criteria. For all alleles and genotypes, odds ratios were pooled using either fixed-effects or random-effects models. An increased odds ratio for type 2 diabetes was observed in persons with the (GT)(n) L (long) allele as compared with those with the (GT)(n) S (short) allele (odds ratio = 1.12, 95% confidence interval: 1.02, 1.24; P = 0.02). Furthermore, the diabetes odds ratio for persons with the LL genotype, versus those with the SS genotype, was significantly increased (odds ratio = 1.25, 95% confidence interval: 1.04, 1.50; P = 0.02). Persons carrying longer (GT)(n) repeats in the HMOX1 gene promoter may have a higher risk of type 2 diabetes.