Oral leukoplakia is the most common pre-malignant oral lesion. It is defined by the WHO as white patch or plaque which cannot be characterized clinically or pathologically as any other disease. If the lesion is red coloured, it is called erythroplakia and if it is a combination of both erythroleukoplakia. The lesion occurs normally after the age of 30 and the prevalence increases with age. Smoke and alcohol abuses are the most important etiological factors. Some viruses, including HPV types, are assumed to be associated with malignant transformation. Ulcerative, verrucous or erosive leuko-/erythroplakias as well as such located on the floor of the mouth or on the tongue have a high malignant tendency. Therapy lies in eliminating potential causes, surgical removal and long-term follow-up's.