It has been reported that abnormal mitotic figures (AMFs) occur principally in aneuploid lesions and that aneuploidy is a diagnostic feature of non-endocrine-dependent epithelial cancer precursors and cancers. Recently, AMFs have been reported in cervical lesions interpreted as flat condylomata, and it has been suggested by several authors that AMFs may not be diagnostic or aneuploidy or neoplasia, particularly in human papillomavirus-(HPV)-induced lesions. Although it is conceivable that AMFs may be a regular feature of HPV infection, their association with cytologic atypia and their presence in higher grades of cervical intraepithelial neoplasia (CIN) suggests that AMFs may herald the presence of a different lesion than the pure flat condyloma. In the current study, koilocytotic cervical lesions thought to be HPV-induced were examined microscopically for the presence of AMFs, and the findings were correlated with the presence of HPV as determined by immunoperoxidase and nuclear DNA distribution patterns as measured by Feulgen microspectrophotometry. In unselected lesions originally diagnosed as flat cervical condylomata, AMFs were surprisingly common (22.6%), and did not correlate with the extent of koilocytosis. Immunoperoxidase (IMPO) stains were performed in 35 cases with AMFs, and were negative for HPV in 74.3% and positive in 22.8%. However, among the cases evaluated by IMPO, there was an inverse relationship between the presence of mitotic abnormalities and the expression of HPV antigen. Nine of 11 (81.8%) lesions containing AMFs were aneuploid, and 2 of 11 (18.2%) were polyploid. Abnormal mitotic figures have a range of morphology and frequency in koilocytotic cervical lesions. Although the biology of these lesions is not well-defined, the presence of AMFs may identify a subgroup of HPV-induced cervical atypias which represent a transition between flat cervical conylomata and CIN.