In a prospective cohort study on the prevalence of HPV in a group of female Swedish students, we obtained repeated cytological specimens during a period of 2 years, for cytological diagnosis and PCR detection of HPV. The group comprised 98 girls, sampled between 15 and 17 years, and 82 of them completed the study. The girls were also followed every sixth month by a structured face-to-face interview regarding sexuality. Only the sexually experienced girls harboured HPV-DNA in the cervix with a cumulative prevalence of 37% and HPV16 was the most common type encountered. Almost half of the infected girls were lacking any clinical or subclinical signs of HPV infection. There was a positive correlation between the presence of HPV and the number of coital partners. The time period since coitarche also had importance for the HPV detection rate.