Oral lichen planus (OLP) is a chronic auto-immune disease associated with cell-mediated immunologic dysfunction whose etiology remains unknown. Malignant transformation into squamous cell carcinoma (SCC) is the most feared complication of OLP. It is actually recognized as a potentially malignant disorder with an unspecified risk of transformation, and it is suggested to closely monitor diagnosed patients.In this paper, we discuss the case of a 62-year-old female patient, a non-smoker, and non-drinker, who initially presented with painful erosive lesions on the edentulous mandibular ridge, the buccal mucosa, and the floor of the mouth. Clinical and histological findings led to the diagnosis of OLP with no signs of oral epithelial dysplasia. Malignant transformation into SCC was reported eight months after the first presentation.