Inter-individual differences in bladder cancer susceptibility may be mediated in part through polymorphic variability in the bioactivation and detoxification of procarcinogens. Glutathione S-transferase mu1 (GSTM1) status has been extensively studied as a risk factor in this context. To clarify the impact of GSTM1 deficiency on bladder cancer risk a meta-analysis of 15 case-control studies from the literature has been carried out using a random effects model. The principal outcome measure was the odds ratio for the risk of bladder cancer. Pooling the studies the odds ratio of bladder cancer risk associated with GSTM1 deficiency was 1.53 (95% confidence limits 1.28-1.84). The relationship between GSTM1 status and bladder cancer risk was not confined to a specific population. This meta-analysis supports the hypothesis that GSTM1 deficiency is a determinant of bladder cancer susceptibility. A review of studies does, however, indicate that greater attention should therefore be paid to the design of future studies. The interaction between GSTM1 and other polymorphisms on the risk of bladder cancer and their interaction with environmental risk factors will only be addressed by well-designed studies based on sample sizes commensurate with the detection of small genotypic risks.