Leukoplakia is the only important precancerous lesion of the mouth. The epidemiology of oral leukoplakia has been well established in white adults in the United States. There is a hole in the epidemiologic literature, however, on leukoplakia in American minority populations. Recent literature has begun to address the issue of the pathophysiology of leukoplakia, its causes and treatment, and predicting its malignant transformation. Computerized image analysis, retinoid compounds, beta-carotene, and laser surgery are contributing to advances in these lines of research. Though leukoplakia is often seen in patients who use smokeless tobacco products, it is usually benign and reversible if use of the tobacco product is discontinued. The direction of current research in leukoplakia studies eventually should lead to an understanding of the nature and cure of this ubiquitous lesion.