An international group of epidemiologists, clinicians and pathologists with a special interest in oral white lesions and their precancerous significance has reviewed earlier work on this topic and identified some of the problems associated with previous definitions, descriptions and classifications. Modifications to these definitions, descriptions and classifications have been proposed, accompanied by explanations of the reasons for identifying the need for changes to be made. Leukoplakia may be a provisional or definitive diagnosis dependent upon the circumstances of oral examination and the availability of other information. Guidelines are provided to assist in the application of the definitions of oral leukoplakia and illustrations depict the homogeneous and non-homogeneous clinical variants. Consideration is also given to the importance of a red component in a white lesion, or a lesion that is entirely red (erythroplakia). A new clinical staging procedure for oral leukoplakia is also proposed.