Lentigo maligna is a lentiginous proliferation of atypical melanocytes confined to the epidermis, typically on chronically sun-damaged skin. Following biopsy and exclusion of invasive disease, therapy may involve Mohs surgery, topical treatment or radiotherapy. However, lentigo maligna often involves adnexal structures, creating histological difficulty in distinguishing these foci from invasive melanoma. We present a case in which, during Mohs excision, a nodule of severely atypical melanocytes appeared to lie within the dermis, potentially altering treatment and prognosis. The use of laminin-5 provided a means of resolving this diagnostic dilemma, facilitating continuation of Mohs surgery until tumour clearance was achieved.