The risk of developing carcinoma of the cervix in women infected with human papillomavirus (HPV) was estimated in a nested case-control analysis of 33 cancers (invasive and in situ) and 113 controls, matched by age and sex, from an ongoing cohort study of lifestyle and cancer in a rural population of Northeast Thailand. Oncogenic HPV types were present in 10.8% of control women and in 31/33 of the carcinoma cases, corresponding to an odds ratio of 130.6 (95% CI 11.7-1457.0). There was no significant difference in risk between prevalent cancer cases (diagnosed less than 3 months after HPV testing) and incident cases (diagnosed an average of 2.1 years later). HPV 16 and 18 were the most prevalent oncogenic HPV types present. The results confirm that some two of three of cervical cancer cases in this population of Northeast Thailand are caused by HPV 16 and 18.