The prevalence of cervical human papillomavirus increases with increasing numbers of sexual partners, leaving the impression that this infection is acquired only as a result of high risk sexual behaviour. Using longitudinal data from 242 women who had only had one sexual partner, we found that the risk of acquiring cervical human papillomavirus infection was 46% (95% CI 28-64) at three years after first intercourse and that the median time from first intercourse to first detection of human papillomavirus was only three months.