Objective: Oral lichen planus (OLP) is a common mucocutaneous disease with malignant transformation potential. The aim of this retrospective study was to investigate the characteristics of patients with OLP who developed oral squamous cell carcinoma (OSCC). Method and Materials: The medical records of 2,119 patients with OLP at West China College of Stomatology, China, from 1951 to 2006, were reviewed. Data were taken from the records of 23 patients with OLP who developed OSCC. Results: The rate of malignant transformation in OLP was 1.1%. The mean age of these patients was 52 years. There were 12 women and 11 men. There was no significant difference between women and men (P = .835). The most common site of malignant transformation was in the tongue (16; 69.57%). The average time from the patient's first visit with OLP to malignant transformation was 16 months (range, 1 to 41 months). More than 50% of patients had alcohol (12; 52.17%) and tobacco (13; 56.52%) habits. Before the malignant transformation, the most frequent symptoms in patients with OLP were pain (21; 91.30%) and erosion (17; 73.91%). Conclusions: The risk of malignant transformation in OLP is real but not high. Erosive OLP in older patients with pain and who use tobacco and alcohol is more likely to exhibit malignant transformation. Keywords: malignant transformation, oral lichen planus, oral squamous cell carcinoma