Introduction This paper reviews epidemiologic studies on prevalence of oral leukoplakia. Special emphasis is placed on population selection, diagnostic criteria, type and training of examiners and risk factor assessment. Prevalence of leukoplakia in these studies has ranged from 0.6% to 4.6%. Variations in prevalence among the studies could depend on methodology, especially studied populations and diagnostic criteria. Most investigations have investigated the entire available adult population in a geographic region or a random sample. Others have comprised selected populations, such as hospital or clinic patients. Our study has shown that prevalence of oral leukoplakia was 2.2% in a relatively small and highly selected population. Age and gender The onset of leukoplakia usually takes place after the age of 30 years. Our study showed that oral leukoplakia occurred in men over 40 years of age and in women over 50 years of age. These results are supported most previous findings. Gender distribution varies in most studies, ranging from a strong male predominance (4:1), to almost 1:1 in the Netherlands. Smoking and prevalence of oral leukoplakia Tobacco smoking is the most important known etiological factor in development of oral leukoplakia. Smokers have a six-fold increase in the risk of developing leukoplakia of the oral mucosa in regard to non-smokers. Six European studies, including our study, found a prevalence of smoking between 56 and 97 percent in leukoplakia patients. Our study also showed that the majority of smokers with leukoplakia (74.0%) smoked more than 20 cigarettes per day compared to 34.5 % of those without leukoplakia. Alcohol and prevalence of oral leukoplakia Smoking and alcohol consumption are often coexistent factors making it difficult to assess the effects of these factors individully. In our study the higest prevalence of leukoplakia (33.3%) was established in subjects who smoked cigarettes and consumed alcohol, compared to those who smoke tobacco only (18.2%).