Papillomatous proliferations of squamous epithelium of the genital and anal region termed Bowenoid Papulosis (BP) macroscopically resemble condylomata acuminata, whereas histologically they show in part severe dysplasias. Despite the similarity of these lesions to Bowen's disease they are - like condylomas - induced by papilloma viruses and may regress spontaneously. Condyloma-like but predominantly flat proliferations of squamous epithelium of the transitional zone between exocervix and endocervix, which are likewise caused by viruses and have a prognosis similar to that of BP, are even more problematic in differential diagnostic differentiation from cervical carcinoma in situ. Both these atypical proliferations of squamous epithelium of the exocervix referred to as "flat condylomas" and BP contain koilocytes as a sign of cell regression relatively typical of virus-induced cell change. In a reported case of a 38-year old woman with widespread BP of the ano-genital region intranuclear papilloma virus antigen could be demonstrated immunohistochemically in the papillomatous proliferations of squamous epithelium and furthermore in sections made from the filed paraffin blocks of a cone biopsy taken five years ago. In two of altogether seven cases of BP presented in tables papilloma virus antigen could be shown as well. In one woman of already 54 years of age widespread BP is described more comprehensively, because due to the feature of inverted papillomatosis carcinoma was suspected clinically. BP and flat condylomas have been defined as terms only in recent years and - as virus-induced lesions - been differentiated from carcinoma in situ on account of a more favourable prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)