The relationship between virus infections of the skin and mucosae and the development of malignant tumors is discussed. Guided by seroepidemiological data, virus infections with herpes simplex have been associated with the development of cervical carcinoma, genomes specific for HSV, however, have only occasionally been detected in malignant tumor tissue from the cervix. In contrast, DNA specific for papilloma virus could be identified to a high percentage in cervical cancerous and precancerous tissue as well as in bowenoid papulosis in both sexes. Aside from oncogenic papilloma virus, malignant degeneration seems to be dependent on both endogenic cofactors such as immunodeficiency and exogenic cofactors like sunlight or additional virus infections.