A 45-year-old man presented with a rapidly enlarging tumour in an area of long-standing hypertrophic lichen planus of the lower leg. Histological examination of the resected specimen showed it to be a giant keratoacanthoma measuring 37 x 57 mm. Neoplastic change is a rarely reported complication of chronic variants of cutaneous lichen planus. To date there have been only two reports of keratoacanthoma development in association with lichen planus.