Schmitz L, et al. – The extent of atypical keratinocytes throughout the epidermis and change in basal growth patterns of actinic keratoses (AK) were scrutinized in this trial. There did not appear to be any link between the basal growth patterns (pro I–III) in AK with the established AK I–III histological grading system. Apart from the degree of upward extension, varying degrees of downward extension existed. Histological classification ought to regard both, upwards and downward growth patterns when assessing AK.