OBJECTIVES: To assess the feasibility of a randomised trial of ovarian cancer screening by vaginal ultrasonography. SETTING: A population based study, recruiting a random sample of the female population aged 46 to 65 years living in Copenhagen, Denmark. DESIGN: Randomised controlled trial allocating 50% to the study group having vaginal ultrasonography, and 50% to the control group having no examination. (a) Acceptability of the study was evaluated by the proportion of eligible women willing to participate in the study. (b) The false positive rate was evaluated as the proportion of women without ovarian cancer referred for an operation because of abnormal ovaries detected by ultrasonography. RESULTS: 950 (64.3%) of the 1477 eligible women participated in the study. At the first scan abnormal ovaries were detected in 54 of 435 women (12%), significantly more frequently among younger women. Nine women were referred for an operation because of abnormal findings in the ovaries, giving a false positive rate of 2%. Ovarian size and morphology found at operation corresponded with those at ultrasonography; none of them was malignant. CONCLUSIONS: A randomised controlled trial of ovarian cancer screening using vaginal ultrasonography seems acceptable in the general population. The rate of abnormal ovaries at ultrasonography with the cut offs used in this study was quite high. Such a study is, therefore, feasible, but it is proposed that it is carried out in an older age group (50-64 years) and that the cut offs used for ovarian size and morphology are re-evaluated. Second line tests, such as colour Doppler flow, should be considered in order to reduce the false positive rate.