To understand the possible likelihood of type-replacement following vaccination against the high-risk human papillomavirus (HPV) types, we evaluated competition of the seven most common genital HPV types in a population sample of 123.773 unvaccinated, fertile-aged Finnish women who consented between 1983-2004. First trimester sera from two consecutive pregnancies were retrieved for a subsample of 3,183 women (mean age 23,1 years) of whom 42,3% had antibodies to at least one of the HPV types 6/11/16/18/31/33/45 at the baseline. Multiple HPV antibody positivity by the second pregnancy was common among both the baseline HPV16 seropositives and HPV18 seropositives. However, highly significantly increased incidence rate ratios (IRR) indicating an increased risk to acquire infection with another HPV type were consistently noted only for HPV type 33 both among the baseline HPV16 seropositive and HPV18 seropositive women: HPV16-33 IRR 3.2 (95% confidence interval, 2.0-5.2) and HPV18-33 IRR 3.6 (95% CI 2.1-5.9), irrespectively whether they had or did not have antibodies also to other HPV types at the baseline: HPV16only-33 IRR 2.9 (95% CI 1.6-5.4) and HPV18only-33 IRR 2.5 (95% 1.1-6.0). Our results indicate a competitive advantage for HPV33 over a number of other genital HPVs in the unvaccinated population. Provided natural infection and vaccine induced immune protection are comparable, our results suggest that HPV33 should be monitored for type-replacement following HPV mass vaccination.