Oral epithelial dysplasia (OED) is one of the common precancerous lesions among Chinese adults. Biomarker is not available for detection of malignant potential of OED till now. p16 is an important tumor suppressor gene, which is inactivated frequently by methylation of CpG island in early stage of carcinogenesis. The present cohort study is to investigate whether p16 methylation is correlated with malignant transformation of OED.