To evaluate KAI1/CD82 expression in Chinese patients with benign prostatic hyperplasia (BPH) and late-stage carcinoma of prostate (CaP).Thirty Chinese patients with benign prostatic hyperplasia and 34 with CaP (adenocarcinoma clinical stage C and D) were analyzed by means of immunohistochemical methods.The KAI1/CD82 expression in BPH tissue was all positive, which was uniformly located on the glandular cell membrane at the cell-to-cell borders, but KAI1/CD82 expression in metastasis CaP tissues was either significantly lower than that of BPH or negative, and the immunostaining pattern was not continuous. In late-stage CaP KAI1/CD82 expression was correlated inversely to the pathological grade ( P0.05), but not to clinical stage ( P0.05).The authors believe that decreased and negative KAI1/CD82 expression in late-stage CaP may be related to tumor progression and metastasis, and appears to be a prognostic marker.