Context: Long-acting reversible contraceptives (LARC) are the most effective means of preventing subsequent abortion, especially if initiated at the time of induced abortion. Medical abortion has replaced the surgical one in many countries; in Finland proportion of medical abortion is up to 96%. Limited data exist on LARC initiation as part of medical abortion service and its long-term effect on the need of subsequent abortion. Objective: To analyze risk factors and effect of post-abortal LARC initiation on the need of subsequent abortion. Methods: Retrospective cohort study. Selected demographic factors, planned contraception and LARC initiation at the time of the index abortion were collected as part of the randomized study assessing post-abortal use of the levonorgestrel-releasing intrauterine system (LNG-IUS), or from patient clinical records. Data on subsequent abortions were retrieved from the electronic patient files of the Hospital District of Helsinki and Uusimaa and the Finnish abortion register. Patients:666 women undergoing medical abortion between February and May 2013 at Helsinki University Hospital, Finland. Intervention:267 women who planned LNG-IUS for post-abortion contraception participated in a randomized study in which they received the LNG-IUS free-of-charge. The other women planned and obtained their post-abortion contraception via the primary health care services. Main Outcome Measure:Risk factors for subsequent abortion. Results: During the follow-up (21 months [median]; interquartile range 20–22) total of 54 (8.1%) women requested a subsequent abortion. When adjusted for age, previous pregnancies, deliveries and induced abortions, as well as gestational-age, planning LARC for post-abortal contraception (33 abortions/360 women, 9.2%) did not prevent subsequent abortion compared to other contraceptive plans (21/306, 6.9%) (HR 1.22, 95%CI 0.68–2.17). However, verified LARC initiation (4 abortions/177 women, 2.3%) decreased the abortion rate compared to women who did not initiate LARC (50/489, 10.2%) (HR 0.17, 95%CI 0.06–0.48). Furthermore, when adjusted also for LARC initiation status, age under 25 years was a risk factor for subsequent abortion (27 abortions/283 women, 9.5%) if compared to women over 25 years (27/383, 7.0%) (HR 1.95, 95%CI 1.04–3.67). Conclusions: Initiation of LARC as part of the abortion service at the time of the medical abortion is an important means to prevent subsequent abortion, especially among young women.