Recently it has been shown that epidermodysplasia verruciformis is induced by human papilloma/virus different from the papilloma/virus of warts, and that 2 distinct viruses-designated HPV-3 and HP-4--are responsible for it. Ten cases of epidermodysplasia verruciformis were found to have been caused by HPV-3. Clinically and histologically, as well as in the often depressed cell-mediated immunity they closely resembled long-standing verrucae planae, also caused by HPV-3. Contrariwise, in epidermodysplasia verruciformis caused by HPV-4 there are characteristic red, red-brown, and depigmented, pityriasis versicolor-like plaques, and malignant transformation seems almost inevitable. Cases due to HPV-3 may be abortive or even regressive, or stationary, and hard to distinguish from flat warts. No malignant conversion was seen in patients infected only with HPV-3, whereas it occurred in 2 patients infected with both viruses: HPV-3 and HPV-4. Pigmented plaques are the most important adverse prognostic sign in EV induced by HPV-3.