On the subtropical island of Okinawa, squamous cell carcinoma (SCC), particularly the well-differentiated form, is the most frequent type of lung cancer, while this form is relatively rare on the Japanese mainland and in other countries. Furthermore, in Okinawa, in 1993, 80% of SCC cases of the lung were found to be infected with human papillomavirus (HPV). We studied the prognosis of SCC of the lung with HPV infection (n = 25) and compared it with non-HPV-infected SCC (n = 16). Using the Kaplan-Meier method (Wilcoxon analysis), the prognosis of HPV-infected cases was found to be better than that of the non-infected cases. In the virus-infected cases, apoptosis and infiltration of a large number of Langerhans cells were demonstrated. In addition to these findings, the virus-infected tumors were demonstrated to be histologically well-differentiated, perhaps contributing to the favorable prognosis. However, among the virus-infected cases, the type 16 virus-infected cases showed a poorer prognosis, compared to those infected with other HPV types. p53 gene mutation was also examined, and was considered to be an unfavorable prognostic factor, as reported elsewhere. However, in Okinawa, HPV-positive cases with p53 mutations showed a slightly better prognosis than did non-viral infected cases with p53 mutations. The TNM staging system was also useful for categorizing the virus-infected cases. The prognosis of stage III (A and B) cases was poor. All of our present cases received surgical treatment. Chemotherapy and radiation therapy were not performed. Such treatment, however, might be effective, because virus-infected uterine cervical carcinomas have been routinely treated with chemotherapy and radiation. Furthermore, if the immunological basis of increased Langerhans cell infiltration in HPV-infected cases is elucidated, a clinical trial with immunotherapy may be favorable for the clinical outcome.