OBJECTIVES: Human papillomavirus (HPV) types 6 and 11 are most commonly associated with ano-genital warts. There are few data on the sero-epidemiology of HPV6 and HPV11 among homosexual men. METHODS: Behavioural data and sera for antibodies to HPV6 and HPV11 capsid protein L1 were collected annually for 1427 HIV negative and 245 HIV positive homosexual men. For HIV negative men, a combined variable, HPV6/11, was created (HPV 6 and/or 11) to analyse predictors of seroprevalence and seroincidence. RESULTS: High rates of HPV6 and HPV11 seroprevalence were found (39.2-53.2% of men). For HPV6/11 (HIV negative men only), seroprevalence was associated with higher numbers of sexual partners, longer history of sexual activity and seropositivity for several sexually transmissible infections. Each year, 12.6% of men younger than 25 years seroconverted. Seroincidence (5.9/100PY) was associated with younger age, more recent male sexual partners, receptive anal fingering and anal chlamydia. Seropositivity and seroconversion were strongly associated with past and incident anal warts. CONCLUSIONS: HPV6 and HPV11 seropositivity were common among homosexual men. Among HIV negative men, HPV6/11 seroprevalence and seroincidence correlated closely with markers of sexual activity. The high numbers of young men seroconverting each year suggests a role for prophylactic vaccination of young gay men. SUMMARY: Ano-genital warts, caused by human papillomavirus, are very common. In a community cohort of Australian homosexual men, HPV6 and 11 seroprevalence and seroincidence were high and were associated with past and incident anal warts and other markers of sexual activity.