Aberrant expression of mismatch repair genes, such as human mutL homolog 1 (hMLH1) and human mutS homolog 2 (hMSH2), are common in some human cancers, and promoter methylation is believed to inactivate expression of hMLH1. We investigated whether promoter methylation is involved in loss of hMLH1 protein and whether aberrant expression of hMLH1 and hMSH2 protein is related to prognosis after resection for esophageal squamous cell cancer.We analyzed promoter methylation of hMLH1 using methylation-specific polymerase chain reaction and hMLH1 and hMSH2 protein by using immunohistochemistry in 60 resected tumor specimens. The Pearson chi2 test was used to compare expression of hMLH1 and hMSH2 protein among patients with different clinicopathologic parameters. Concordance analysis was performed between hMLH1 methylation and its protein expression.Loss of hMLH1 and hMSH2 protein was found in 43 (72%) and 39 (65%, P = .06) of 60 resected specimens, respectively. hMLH1 protein correlated well with tumor staging (P < .0001), depth of tumor invasion (P = .008), and nodal involvement (P < .0001) but not with distant metastasis, whereas hMSH2 did not show correlation with any of these parameters. A concordance rate of 83.3% was present between expression of hMLH1 protein and its promoter methylation (P < .001).Aberrant expression of hMLH1 and hMSH2 protein is frequently associated with the presence of esophageal squamous cell carcinoma, and expression of hMLH1 protein is a better prognostic predictor than is expression of hMSH2 protein. Promoter methylation is one of the mechanisms responsible for loss of hMLH1 protein in esophageal squamous cell cancer.