Statistical considerations: Sample size calculation: Assuming the incidence of HSIL is 5 and 15 per cent 100 person-years in HIV negative and HIV positive men, respectively, the 95% confidence intervals will be 4.2-6.0 in the HIV negative arm and 12.6-17.8 per 100 person-years in the HIV positive arm. Analysis plan: HPV prevalence and incidence, including overall, low risk, high risk and individual types, will be calculated according to participant's HIV status. Prevalence and incidence of LSIL and HISL will be calculated in the same fashion. Clearance and persistence of HPV infection, and progression and regression of HSIL will also be determined. Risk factors for prevalent HPV infection and LSIL and HSIL will be analysed using logistical regression. Risk factors for incident conditions will be analysed using Cox regression.