As AIN and cancer precursor lesions of the cervix, cervical intraepithelial neoplasia, share distinct clinical similarities, cytologic smear testing for AIN has been recommended to detect and treat early lesions. Thus, this prospective study mainly focuses on the predictive value of HPV-DNA load for the development and clinical progression of AIN in HIV-infected MSM. Moreover, the course of HPV viral load under therapy for anal intraepithelial neoplasia, e.g. topical treatment with imiquimod, will be evaluated. Additionally, immunohistochemical determination of several proliferative biomarkers, as well as cytokines, will be performed.