After considering the leukoplakia as defined by the WHO, the authors examine the quantitative, qualitative, histopathologic and clinical aspects of leukoplastic lesions. Afterwards, the data concerning the incidence of the malignant evolution of leukoplakia are shown. Data that have been collected and shown during years of study and that are often discordant. For this reason a study on the literature since 1931 is carried out and all the possible causes that could have led to different results are mentioned. Than the authors, among 98 cases of leukoplakia, examine those that turned malignant. In five cases, after the first biopsy, the histopathological report found the presence of microcarcinoma while, in three other cases, in the follow-up, a malignant evolution was observed. This This study points out a percentage of malignant transformation of the leukoplakia equal to 2,94% in agreement with the study of Pindborg and Banoczy.