The emergence of epidermal epitheliomas in the scars of patients with polydysplastic epidermolysis bullosa is the result of a carcinogenic process similar to that observed in the scars of thermal burns and other chronic cicatrices. In three of the four cases, the patients developed multiple, well-differentiated squamous-cell cancers; in one patient basal-cell epitheliomas were also present. Confirmation of cancer histologically was difficult because of limitations in distinguishing pseudoepitheliomatous hyperplasia from squamous-cell cancer. There was no doubt of carcinomatous conversion biologically, however, as metastases occurred in the patients. Therapy was inadequate; and despite its limitations, surgery seems to be the treatment of choice.