Objective To compare use of the copper intrauterine device (IUD) after immediate compared to delayed insertion following medical abortion (MA) at 17-20 gestational weeks (GW). Design Randomized controlled trial Setting One tertiary hospital and five community healthcare centres in South Africa Population Women admitted August 2018 to June 2019 for elective MA at 17-20 GW Methods Women were randomized to immediate (within 24 hours) or delayed (3 weeks post-abortion) insertion of the copper IUD. Follow-up was at 6 weeks, 3 and 6 months. Study outcomes were compared by intention-to-treat (ITT) and per-protocol analyses. Main outcomes Use of the original IUD, and use of any IUD at 6 weeks post-abortion (ITT) Results In the immediate (n=55) and delayed arms (n=57) respectively, 82% and 21% received the IUD as planned. By ITT, 56% in the immediate and 19% in the delayed arms were using the original IUD at six weeks (p<0.001), 76% in the immediate and 40% in the delayed arms were using any IUD (p<0.001). Loss-to-follow-up at 6 weeks was 2%. Complete expulsion or removal occurred in 14 (31%) in the immediate and 1 (7%) in the delayed arms (p=0.004). Conclusions Insertion of an IUD immediately after MA at 17-20 GW results in increased use after 6 weeks compared to delayed insertion. Expulsion rates are higher than interval insertion and immediate insertion at earlier gestation, but similar to immediate postpartum insertion. Key words Second trimester, medical abortion, IUD Clinical trials registration: clinicaltrials.gov/ (ID NCT03505047), Pan African Trials Registry (www.pactr.org), ID PACTR201804003324963