Cervical-cancer screening programmes using cytomorphological criteria could be more efficient if the screening included objective individual risk factors for women with normal cytology, such as a test for high-risk human papillomavirus (HPV). The value of a PCR-based test for high-risk HPV types was studied in a cohort of 1622 women presenting in a routine triannual population-based screening programme. Women were included in the study when they had no previous history of cervical dysplasia; and their initial Pap smear was read as normal (Pap 1 or 2). The mean age of the women was 42 years (range 34-54 years) and mean follow-up time was 40 months (range 5-73 months). Women were referred for colposcopically directed biopsies if they had had 2 successive cervical smears read as Pap 3a (mild to moderate dyskaryosis) or one read as > or = Pap 3b (severe dyskaryosis). Women with histologically confirmed cervical intraepithelial neoplasia grade III (CIN III) were considered positive cases. All women were tested for 14 high-risk HPV genotypes. Of the 86 high-risk HPV-positive women, 6 developed CIN III, whereas only 1 of the 1536 HPV-negative women did. The women with normal Pap smears containing high-risk HPV genotypes were 116 times (95% CI, 13-990) more at risk of developing CIN III, in contrast to women without high-risk HPV. These results support the view that the interval between successive smears in cervical-cancer screening can be increased considerably for women with cytomorphologically normal and high-risk HPV-negative cervical smears as determined by PCR.