Objective To assess the 1‐year continuation rates and new pregnancies following immediate versus delayed insertion of the levonorgestrel‐releasing intrauterine system (LNG‐IUS) after medical termination of pregnancy (MTOP) up to 20 weeks of gestation. Design A randomised controlled trial. Setting Helsinki University Hospital, Finland, January 2013 to December 2014. Population A total of 267 women requesting MTOP and planning LNG‐IUS for post‐MTOP contraception. Methods Insertion of LNG‐IUS occurred immediately (0–3 days) or after a delay (2–4 weeks) following MTOP. Follow‐up visits were at 3 months and 1 year after MTOP. Main outcome measures LNG‐IUS use at 1 year after MTOP. Results Women were randomised to immediate (n = 134) or delayed (n = 133) insertion of the LNG‐IUS, and 133 and 131 were analysed; 127 (95.5%) women received immediate insertion and 111 (84.7%) women had delayed insertion of the LNG‐IUS (risk ratio RR 1.13, 95% CI 1.04–1.22). The verified numbers of women continuing the LNG‐IUS use at 1 year were 83 (62.4%) and 52 (39.7%) (RR 1.57, 95% CI 1.23–2.02). The numbers of new pregnancies were 6 (4.5%) and 16 (12.2%) (RR 0.37, 95% CI 0.15–0.91), and numbers of subsequent TOPs were 4 (3.0%) and 5 (3.8%) (RR 0.79, 95% CI 0.22–2.87). Conclusions Immediate insertion of the LNG‐IUS following MTOP resulted in higher 1‐year continuation rates compared with delayed insertion. In addition, those receiving immediate insertion demonstrated a decreased new pregnancy rate, but no difference in the numbers of another TOP. Tweetable Immediate LNG‐IUS insertion after MTOP results in a higher 1‐year continuation compared with delayed insertion. Tweetable Immediate LNG‐IUS insertion after MTOP results in a higher 1‐year continuation compared with delayed insertion.