To evaluate human papillomavirus (HPV) testing in combination with cytology in the follow up of treated women. A prospective study. Three UK centres: Manchester, Aberdeen and London. Women treated for cervical intraepithelial neoplasia (CIN). Women were recruited at 6 months of follow up, and cytology and HPV testing was carried out at 6 and 12 months. If either or both results were positive, colposcopy and if appropriate, a biopsy and retreatment was performed. At 24 months, cytology alone was performed. Cytology and histology at 6, 12 and 24 months. Nine hundred and seventeen women were recruited at 6 months of follow up, with 778 (85%) and 707 (77.1%) being recruited at 12 and 24 months, respectively. At recruitment, 700 women had had high-grade CIN (grades 2 or 3) and 217 had CIN1. At 6 months, 14.6% were HPV positive and 10.7% had non-negative cytology. Of those with negative cytology, 9% were HPV positive. Of the 744 women who were cytology negative/HPV negative at baseline, 3 women with CIN2, 1 with CIN3, 1 with cancer and 1 with vaginal intraepithelial neoplasia (VAIN)1 were identified at 24 months. Nine of 10 cases of CIN3/cervical glandular intraepithelial neoplasia (CGIN) occurred in HPV-positive women. At 23 months, cancer was identified in a woman treated for CGIN with clear resection margins, who had been cytology negative/HPV negative at both 6 and 12 months. Women who are cytology negative and HPV negative at 6 months after treatment for CIN can safely be returned to 3-year recall.