BACKGROUND: Long-term follow-up of large cohorts is needed to determine the effects of HPV and screening on CIN3 (grade 3 cervical intraepithelial neoplasia) and ICC (invasive cervical cancer). METHODS: Women were recruited when attending for routine cervical screening in Greater Manchester, UK: 1987-93 for the Manchester Cohort (MC: 47,625 women) and 2001-03 for the ARTISTIC Cohort (AC: 24,496 women). Both were followed through national registration for cancer incidence and mortality to 2020. RESULTS: Risk patterns following HPV infection differed for CIN3 and ICC. Risk of ICC in the MC rises for 30 years following a single positive HPV test, reaching 2.5% (95% CI: 1.3-4.5%). A similar pattern was seen in the AC, but the risks of cancer were approximately halved. CIN3 was diagnosed much sooner in the AC due to more efficient cytology. More sensitive HPV testing was able to better predict future risk. CONCLUSION: The sensitivity of HPV testing and cytology influences the CIN3 detection rate. Sensitive HPV testing enables effective risk stratification. Increased risk of ICC is observed 15-30 years after HPV infection. Women testing HPV + should be followed until their infection clears. Discharging women from screening programmes whilst they remain HPV + may not be safe, even if cytology and colposcopy tests are normal.