Absence of Human Papillomavirus DNA in Nongenital Seborrheic KeratosisSeborrheic keratosis (SK) is a benign epidermal tumor of unknown etiology. Because of its wart-like morphology, human papillomavirus (HPV) has been suggested as a possible causative agent. Viral involvement, however, has not been confirmed yet despite extensive research. The aim of this study was to evaluate the presence of HPV 6/11, 31, 33 DNA in nongenital SK. We analyzed 40 biopsy specimens taken from patients with nongenital SK using in situ polymerase chain reaction (PCR) and PCR with tissue extracts. The SK specimens (n=40), analyzed by in situ PCR, were negative for all HPV probes tested (types 6/11, 31, 33). Control slides (condyloma acuminatum, n=3) were positive for type 6/11, 31, and 33 HPV probes tested. Melasma samples (n=4), the negative controls, were consistently negative. No HPV DNA band was detected by PCR with the tissue extracts from paraffin-embedded SK samples, while condyloma acuminatum, the positive controls, showed DNA bands of the correct molecular weights. Our results show that HPV type 6/11, 31, and 33 cannot be recognized as causative agents for nongenital SK, which is in contrast to the previous studies. Further studies are required to reveal the presence of other types (more than 90) of HPV DNA.