Flat warts (condylomata) of the uterine cervix are sometimes cytologically atypical and have abnormal mitotic figures; they are thought to be possible precursors of cancer of the cervix. Flat warts are caused by any of a number of types of human papillomaviruses (HPVs), one of which (HPV 16) has been previously associated with invasive cancer of the cervix. To determine whether HPV 16 is also associated with flat warts with abnormal mitoses, we analyzed 23 flat warts by DNA-hybridization techniques for the presence of HPV 16 and other HPV types, and correlated the results with the histology. Of 10 lesions with abnormal mitotic figures, 7 contained HPV 16, and 1 contained another type of HPV. Of 13 lesions without abnormal mitotic figures, only 1 contained HPV 16, and 7 contained other types of HPV. We conclude that the presence of HPV 16 correlates with the presence of abnormal mitotic figures in flat warts of the cervix, and that this type of flat wart is a precursor of invasive cancer of the cervix.