OBJECTIVE: The United Kingdom Collaborative Trial of Ovarian Cancer Screening (UKCTOCS) aims to establish the efficacy of 2 different ovarian cancer screening schedules. The psychosocial substudy examines the psychological factors associated with the screening program. METHODS: Women aged 50 to 75 years from 16 UK gynecologic centers randomized to annual multimodal screening or ultrasound screening (US) groups were followed up for 7 years. Psychosocial data from women who withdrew from the study after a repeat screen were examined. RESULTS: Sixteen percent (3499/21,733) of women requiring a repeat screening test in addition to annual screen withdrew from the study: 12.9% (1560/12,073) from the multimodal group and 20.1% (1939/9660) from the US group. An estimated relative risk of withdrawal is 1.46 (95% confidence interval, 1.36-1.56; P ≤ 0.001) for the US arm. High anxiety trait and increased psychological morbidity significantly influenced withdrawal, even when age, screening center, and group were taken into account (P < 0.001). The risk of withdrawal decreased significantly the longer a woman stayed in UKCTOCS, irrespective of the number of screens and intensity in the preceding year. CONCLUSIONS: Withdrawal rate was greater in women undergoing US screening and in those who had repeats earlier in UKCTOCS. Having a high predisposition to anxiety, high current state anxiety, and above threshold general psychological morbidity all increased the withdrawal rate.