Background. Whether some benign ovarian cysts can develop into cancerous cysts is not known. If a large proportion of ovarian cancers arose in this way, it might be possible to remove the benign cysts in a screening programme before they became malignant. We used follow-up data from a cohort of 5479 self-referred women without symptoms, who participated in a ultrasonographic-screening trial for early ovarian cancer between June, 1981, and August, 1987. We assessed whether the removal of persistent ovarian cysts from these women was associated with a reduction in the expected number of deaths from ovarian cancer in the cohort as a whole. Methods. The expected number of deaths from all causes, all cancers, and ovarian, breast, and colorectal cancers were calculated for the study cohort by the standard life-table method. The actual number of deaths and each cause were obtained and the proportional mortality ratio was calculated for each cause of death. Findings. 5135 (95%) of the participants in the original trial were traced. During the screening, five of these women were found to have stage I epithelial ovarian cancer and 88 had benign epithelial ovarian tumours. The number of reported deaths from all causes (387 [50% of expected]), all cancers (221 [71%]), and ovarian cancer (22 [90%]) was lower than expected because of the 'healthy-volunteer effect'. Proportional mortality ratios were 100% (by definition) for all cancers, 141% for breast cancer, 128% for ovarian cancer (95% CI 87.7-187.6, p = 0.19), 84% for colorectal cancer, and 48% for lung cancer. Interpretation. The removal of persistent ovarian cysts was not associated with a decrease in the proportion of expected deaths from ovarian cancer relative to other cancers during follow-up. For population-based screening of healthy women without a family history of ovarian cancer, a screening test is required that is specific and sensitive to early malignant disease, and inexpensive.