OBJECTIVE It is assumed that the circulation of HPV types in a population is stable over time although there are limited historical data to support this view. The existence of possible cohort effects in the circulation of HPV types has major implications for vaccination strategies and risk assessment in HPV-infected women. We analysed archival biopsy samples of cervical intraepithelial neoplasia (CIN) to study the distribution of HPV types in Northern Italy over the years 1985-2007. METHODS DNA from formalin-fixed paraffin-embedded cervical biopsies from the years 1985-87 (67 samples) and 1995-97 (92 samples) was HPV-typed by the SPF-(10) Lipa assay. Cases were compared with 159 control biopsies from the years 2005-07 matched by patient age and CIN grade. Quantitative PCR was used to compare titres of HPV sequences in DNA extracted from biopsies of the three periods. Type-specific PCR was used to confirm HPV51 and 52 typing by SPF-(10) Lipa. RESULTS HPV51, 52, 53, 56, 58, and 66 were markedly under-represented or undetectable in samples from past periods whereas they represented 5.7-30.8% of present infections. Frequency of multiple HPV infections and high-risk infections (p=0.0001) also increased in recent years. The main changes occurred over the last decade. Infections by HPV16, 18, were three times more frequent 20 years ago than today (p=0.012). Loss of amplifiable HPV sequences over prolonged storage was not observed. Type-specific PCR confirmed all HPV51 and 52 infections. CONCLUSIONS Secular trends in the distribution of HPV types among women with CIN may occur in specific populations.