An age-based pattern of human papillomavirus (HPV) was observed among unvaccinated women in Australia, with a second peak occurring when women were in their early 50s. A similar age-based pattern for genital warts was also observed among unvaccinated Australian women, with the first peak (8.4%) occurring at age 15-20 years, which then declined gradually to 4.8% when women were aged 41-45 years; this then increased to 5.4% when women were aged 46-50 years. This data suggests that behavioural factors may explain the changes in HPV occurrence.