Oral potentially malignant disorders (OPMDs) are precursor lesions that may undergo malignant transformation to oral cancer. These lesions most commonly present clinically as white patches (leukoplakia). However, they may also be red (erythroplakia), or red and white (erythroleukoplakia). There are many risk factors associated with the development of an OPMD, and with the risk of malignant transformation of the lesion. A biopsy with subsequent microscopic examination from the lesional tissue is necessary in identification of OPMD. This article reviews the clinical appearance of OPMDs, associated risk factors, diagnosis and histologic appearance, and treatment.