Squamous cell carcinoma complicating lichen planus is described in 3 patients. In 2, the cancers developed on the lower leg in chronic and hypertrophic lichen planus. In the other case, the cancer complicated lichen planus of the lip mucosa in a smoker. In the two cutaneous cases, the tumour and the adjacent skin showed features of lichen planus, including hypergranulosis, cytoid bodies and a lichenoid infiltrate. The association, though rare with cutaneous lichen planus when it tends to affect chronic hypertrophic lesions on the lower legs, is now well recognized with oral lichen planus. Patients with oral involvement warrant long-term follow-up, especially if they have other risk factors such as smoking or excessive ultraviolet exposure. Chronicity of lichen planus at other skin sites may also be a risk factor.