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Epidemiological studies have evaluated the association between catechol-O-methyltransferase (COMT) Val108/158Met polymorphism and breast cancer risk. However, the results remain conflicting rather than conclusive. In order to derive a more precise estimation of the relationship, we performed this meta-analysis. Systematic searches of the PubMed and Medline databases were performed. A total of 41 studies including 25,627 cases and 34,222 controls were identified. Genotype distributions of COMT in the controls of all studies were in agreement with the Hardy-Weinberg equilibrium (HWE) except for three studies. When all 41 studies were pooled into the meta-analysis, there was no evidence for significant association between COMT Val108/158Met polymorphism and breast cancer risk (for Val/Met vs. Val/Val: OR = 0.99, 95% CI = 0.93-1.04; for Met/Met vs. Val/Val: OR = 0.96, 95% CI = 0.88-1.04; for dominant model: OR = 0.97, 95% CI = 0.92-1.03; for recessive model: OR = 0.97, 95% CI = 0.90-1.04). In the subgroup analyses by ethnicity, menopausal status, no significant associations were found in all genetic models. When sensitivity analyses were performed by excluding HWE-violating studies, all the results were not materially altered. In summary, the meta-analysis strongly suggests that COMT Val108/158Met polymorphism is not associated with increased breast cancer risk.