It is valuable to establish a population-based prevaccination baseline distribution of human papillomavirus (HPV) types among women with high-grade cervical intraepithelial neoplasia (CIN) grade 2 or 3 and cervical cancer in order to assess the potential impact of HPV vaccination. In four countries (Denmark, Norway, Sweden, and Iceland), we collected consecutive series of cervical cancers (n = 639) and high-grade precancerous cervical lesions (n = 1240) during 2004-2006 before implementation of HPV vaccination and subjected the specimens to standardized HPV genotyping. The HPV prevalence was 82.7% (95% confidence interval [CI] 79.0-86.4) in CIN2, 91.6% (95% CI 89.7-93.5) in CIN3, and 86.4% (95% CI 83.7-89.1) in cervical cancer. The most common HPV types in CIN2/3 were HPV16 (CIN2: 35.9%, 95% CI 31.2-40.6; CIN3: 50.2%, 95% CI 46.8-53.6) and HPV31 (CIN2: 10.9%, 95% CI 7.8-13.9; CIN3: 12.1%, 95% CI 9.9-14.3), while HPV16 and HPV18 were the most frequent types in cervical cancer (48.8%, 95% CI 44.9-52.7 and 15.3%, 95% CI 12.5-18.1, respectively). The prevalence of HPV16/18 decreased with increasing age at diagnosis in both CIN2/3 and cervical cancer (P < 0.0001). Elimination of HPV16/18 by vaccination is predicted to prevent 42% (95% CI 37.0-46.7) of CIN2, 57% (95% CI 53.8-60.5) of CIN3 and 64% (95% CI 60.3-67.7) of cervical cancer. Prevention of the five additional HPV types HPV31/33/45/52/58 would increase the protection to 68% (95% CI 63.0-72.2) in CIN2, 85% (95% CI 82.4-87.2) in CIN3 and 80% (95% CI 77.0-83.2) in cervical cancer. This study provides large-scale and representative baselines for assessing and evaluating the population-based preventive impact of HPV vaccination.