Glutathione S-transferase M1 (GSTM1) might be involved in inactivation of procarcinogens that contribute to the genesis and progression of cancers. GSTM1 null status has been extensively studied as a risk factor in bladder cancer susceptibility. The aim of this study is to evaluate the role of GSTM1 null genotype in bladder cancer risk. All available studies were considered in this meta-analysis, including 7301 cases and 9405 controls from 33 studies. Significantly increased risk was detected between GSTM1 deletion and bladder cancer susceptibility in all subjects (odds ratio [OR] = 1.409 [1.267-1.568], P < 0.001). The same patterns were observed in Caucasians (OR = 1.434 [1.212-1.697], P < 0.001) and Asians (OR = 1.485 [1.295-1.704], P < 0.001). When stratified with study design, a positive association was also found in hospital-based studies (OR = 1.552 [1.382-1.744], P < 0.001), but no association in population-based ones (OR = 1.088 [0.970-1.221], P = 0.151). In summary, our meta-analysis suggested that GSTM1 null status is associated with a high increase in the risk of bladder cancer, and further studies based on population design are necessary to confirm our conclusion.