OBJECTIVES: To predict the incremental lifetime effects, costs, and cost effectiveness of using human papillomavirus testing to triage women with borderline or mildly dyskaryotic cervical smear results for immediate colposcopy. DESIGN: Modelling study. SETTING: Three centres participating in NHS pilot studies, United Kingdom. Population Women aged 25-64 with borderline or mildly dyskaryotic cervical smear results. INTERVENTIONS: Screening using conventional cytology, liquid based cytology, and four strategies with different age cut-off points and follow up times that used combined liquid based cytology and human papillomavirus testing (adjunctive human papillomavirus testing). RESULTS: The model predicts that compared with using conventional cytology without testing for human papillomavirus, testing for the virus in conjunction with liquid based cytology for women with borderline or mildly dyskaryotic cervical smear results (aged 35 or more) would cost 3735 pounds sterling (5528 euros; 6474 dollars) per life year saved. Extending adjunctive human papillomavirus testing in combination with liquid based cytology to include women aged between 25 and 34 costs an additional 4233 pounds sterling per life year saved. Human papillomavirus testing is likely to reduce lifetime repeat smears by 52%-86% but increase lifetime colposcopies by 64%-138%. CONCLUSIONS: Testing for human papillomavirus to manage all women with borderline or mildly dyskaryotic cervical smear results is likely to be cost effective. The predicted increase in lifetime colposcopies, however, deserves careful consideration.