Anal cancer is uncommon in the general population, although it is increasing in incidence. It is the second most closely HPV-related cancer, after cervical cancer. Anal cancer incidence is heavily concentrated in gay and bisexual men, people with HIV, solid organ transplant recipients and in women with previous genital HPV-related disease.  In the highest risk population, gay men with HIV, annual incidence reaches over 100/100,000, making it one of the most common of any cancers in this population.

A cytology-based screening program has been proposed, based on the cervical cancer analogy, but substantial questions remain, including about the natural history of anal HPV infection and associated squamous intra-epithelial lesions (SIL). In response to this uncertainty, we set up a 3-year cohort study of anal HPV and SIL in HIV-positive and HIV-negative gay men aged 35 and older in Sydney. Six hundred and seventeen men were enrolled and are currently under follow up. Data of relevance to the design and conduct of a potential future anal cancer screening program will be presented.