BACKGROUND Increasing gestational age is associated with an increased risk of complications in studies assessing surgical termination of pregnancy (TOP). Medical TOP is widely used during the second trimester and little is known about the frequency of complications. This epidemiological study was undertaken to assess the frequency of adverse events following the second trimester medical TOP and to compare it with that after first trimester medical TOP. METHODS This register-based cohort study covered 18 248 women who underwent medical TOP in Finland between 1 January 2003 and 31 December 2006. The women were identified from the Abortion Registry. Adverse events related to medical TOP within 6 weeks were obtained from the Hospital Discharge Registry. RESULTS When compared with first trimester medical TOP, second trimester medical TOP increased the risk of surgical evacuation [Adj. odds ratio (OR) 7.8; 95% confidence interval (CI) 6.8-8.9], especially immediately after fetal expulsion (Adj. OR 15.2; 95% CI 12.8-18.0). The risk of infection was also elevated (Adj. OR 2.1; 95% CI 1.5-2.9). Within the second trimester, increased length of gestation did not influence the risk of surgical evacuation or infection after medical TOP. CONCLUSIONS Medical TOP during the second trimester is generally safe. Surgical evacuation of the uterus is avoided in about two-thirds of cases, though it is much more common than after first trimester medical TOP. The risks of surgical evacuation and infection do not increase with gestational weeks in the second trimester TOP.