Studies investigating the association between glutathione S-transferase M1 (GSTM1) polymorphism and bladder cancer risk report conflicting results. The objective of this study was to quantitatively summarize the evidence for such a relationship. We performed a systematic search of the National Library of Medline and Embase databases. This meta-analysis included 26 case-control studies, which included 5029 bladder cancer cases and 6680 controls. The combined results based on all studies showed that the GSTM1 null genotype was associated with an increased risk of bladder cancer (OR=1.46, 95% confidence interval [CI]=1.35, 1.57). When stratifying for race, results were similar among Asians (OR=1.60, 95% CI=1.27, 2.01) and Caucasians (OR=1.44, 95% CI=1.33, 1.57) except Africans (OR=1.25, 95% CI=0.76, 2.06). When stratifying by the smoking, stage, grade, and histological type of bladder cancer, we found no statistical association. Our meta-analysis suggests that the GSTM1 null genotype is associated with a modest increase in the risk of bladder cancer.