Oral leukoplakia is defined as “a predominantly white lesion of the oral mucosa that cannot be characterized as any other definable lesion”. Leukoplakia is used only as a clinical term and is classified histopathologically into hyperkeratosis, dysplasia, carcinoma in situ, and invasive carcinoma. As multistep carcinogenesis is the common process by which malignant neoplasms are generated, one leukoplakia may have “mixed” different histopathological states such as hyperkeratosis, dysplasia, and invasive carcinoma. Local biopsy at an unsuitable site might lead to under-diagnosis and hence suboptimal treatment. The purpose of this study was to investigate the effect of total excision of tongue leukoplakia for histopathological diagnosis. Twenty-eight cases of tongue leukoplakia treated during the past 13 years were enrolled in this study and were divided into two groups: 1) 10 cases examined by local biopsy before total excision and 2) 18 cases treated by total excision without local biopsy. In the first group, there were 4 cases (40%) having a histopathological diagnostic mismatch between local biopsy and surgical excision afterward. Three cases were pathologically “mixed” cases in which an unsuitable site was biopsied, and one case was biopsied at only a superficial site. In the second group, 6 cases (33%) had pathologically “mixed” states. In conclusion, total excision should be performed for the diagnosis of tongue leukoplakia because local biopsy may lead to under-diagnosis.