Abstract Background: Uptake in the English Bowel Scope Screening Programme is below the European target for acceptable participation. The aim of this study was to test the impact of sending non-participants a self-referral reminder 12 and 24 months after their initial invitation. Methods: Eligible adults were men and women in London who had not attended a BSS appointment within 12 months of their initial invitation. Individuals were randomised (1:1:1) to receive either: no reminder (control), a self-referral reminder and standard information booklet (Rem-SIB), or a self-referral reminder and theory-based leaflet designed to address barriers to uptake (Rem-TBL). Anyone not screened within 12 months was re-sent the reminder and corresponding leaflet 24 months after the initial invitation. The primary outcome was the proportion of adults screened within each group 12 weeks after the 24 month reminder was sent.Results: 1383 former non-participants were randomised and analysed as allocated (n=461 per arm). Uptake was 0.7%, 14.5% and 21.5% in the control, Rem-SIB and Rem-TBL groups respectively. Individuals in the Rem-SIB and Rem-TBL groups were significantly more likely to attend screening than individuals in the control group (aOR=26.1, 95% CI=8.1-84.0, P<0.001 and, aOR=46.9, 95% CI=14.7-149.9, P<0.001 respectively). Individuals in the Rem-TBL group were also significantly more likely to attend screening than individuals in the Rem-SIB group (aOR=1.87, 95% CI: 1.3-2.6, P<0.01). Conclusion: Reminders targeting non-participants at 12 and 24 months improve uptake and are enhanced by the inclusion of a theory-based leaflet designed to address barriers to participation. External funding details St Marks HospitalCancer Research UK