White lesions of the oral mucosa may be caused by various disorders. In most instances of white lesions, diagnoses can be made solely on clinical grounds. When the clinical diagnosis is not compatible with a known disease, the term leukoplakia is used. This is of importance since the yearly malignant transformation rate of oral leukoplakia into a squamous cell carcinoma is 2-4%. The presence and degree of epithelial dysplasia is the most important predictor for malignant transformation.