BACKGROUND The histological and immunohistochemical evaluation of tissue samples obtained in the course of the investigation and treatment of precancerous squamous lesions of the cervix uteri is an essential task of the pathologist. Given the surprising variety of morphological findings, including the many possible differential diagnoses of dysplastic changes, this is not an easy task. Biologically, only two prognostically different groups can be distinguished, which according to the WHO classification are referred to as low-grade or high-grade squamous intraepithelial lesions (LSILs or HSILs). An additional distinction as CIN1, CIN2 or CIN3 should also be made, in particular because CIN2 lesions represent a  heterogeneous group of dysplastic changes. The p16 biomarker, which has been widely studied, is extremely helpful in the diagnosis and differential diagnosis of these lesions, as regenerative and reparative changes as well as non-HPV-associated squamous cell metaplasia, are p16 negative or show patchy staining only. The indications for its use were clearly defined in the LAST project. In contrast to the diagnostic advantage, the prognostic significance of p16 in the low-grade intraepithelial lesions is controversial. Other markers such as CK7 and HPVE4 may help here. The immunohistochemistry for p16 may also be useful in examining the resection margins of a conization specimen, especially if thermoeffects make it difficult to make an unambiguous assessment. However, for the prognostic assessment of the clinical course after conization, the HPV test is more important because it better captures the risk of persistence or the risk of recurrence.