Background: LL-37 is a peptide belonging to the cathelicidin family of antimicrobial peptides. Recent investigations have suggested that the expression of antimicrobial peptides is an important mechanism for resistance to microbial infection. Objective: The aim of this study was to determine whether LL-37 is expressed in papillomavirus-infected epidermis from patients with condyloma acuminatum or verruca vulgaris. Methods: Biopsy specimens from 3 patients with condyloma and 2 patients with verruca vulgaris and 6 normal skin samples were studied by immunostaining with an antibody specific to LL-37 and control rabbit serum. Western blots were performed on skin extracts from normal skin and verrucae. Results: A large increase in the expression of LL-37 was seen within keratinocytes of all involved samples and in the extracts of verrucae analyzed by Western blot. Conclusion: This study shows the antimicrobial peptide LL-37 is induced within the epidermis during the development of verruca vulgaris. This expression represents a previously unknown immunologic response to papillomavirus infection and may represent an important step in the pathogenesis of this disorder. (J Am Acad Dermatol 2002;47:347-50.)