Oral lichen planus (LP) is a relatively common disorder of unknown aetiology. Oral LP occurs most often on the buccal mucosa, but the gingivae, tongue, floor of the mouth, retromalar pads and lips may also be affected. Usually, patients have multiple sites of involvement. We report a 44-year-old patient with a 3-year history of isolated swelling of the lower lip, erosions and crusting. Histology of a biopsy from the lip revealed features of LP. Oral treatment with acitretin and low-dose steroid led to complete resolution of the lesions within 10 weeks. This is the first well-documented case of isolated LP of the lip. Diagnostic difficulties and differential diagnosis are reviewed.