The most important complication of oral lichen planus (OLP) is the development of squamous cell carcinoma (SCC)--this being an association that remains subject to controversy. This study aims to examine the incidence and clinical presentation of oral malignancies associated with OLP. A retrospective study was made of 550 patients diagnosed with OLP according to the criteria of the World Health Organization, in the period between 1991 and 2007, in south-eastern Spain 128 males (23.3%) and 422 females (76.7%). A clinical protocol was applied in all cases (sociodemographic data, habits and hepatitis C markers), with histological confirmation of the disease. Five of the 550 patients (0.9%) developed SCC. The mean duration of follow-up was 24+/-20.83 months. The tongue was the most common location. The exact incidence of malignant transformation of OLP is difficult to establish, due to the possible contribution of external risk factors that may be of relevance in oral malignancy.