Proliferating cell nuclear antigen (PCNA), nuclear DNA content and mutant p53 overexpression were studied by means of image cytometry and immunohistochemistry respectively in normal mucosa (n = 10), in mild (n = 16), moderate (n = 9) and severe (n = 17) atypical lesions, as well as in squamous cell carcinomas (n = 36) of the cervix uteri. The results show that increasing histopathological atypia in the cervical mucosa was correlated to an initial increase of PCNA followed by distinct aneuploidy and p53 overexpression. The data are suggested to contribute to a better understanding of the genesis of cervical carcinoma, and to indicate that the coexistence of both distinct aneuploidy and p53 immunoreactivity can be used to decide if a cell population is neoplastic, whereas the absence of p53 overexpression does not necessarily exclude neoplasia. This diagnostic procedure can be suggested to improve early detection of intraepithelial squamous neoplasia.