Objectives To compare the efficacy of repeated doses of 100g vs. 200g misoprostol given sublingually for induction of second trimester abortion. Methods One hundred and sixty-two women at 15-22 weeks' gestation were randomized to receive every 2h either 100g (group 1; n=81) or 200g (group 2; n=81) misoprostol sublingually. The primary outcome measure was the abortion rate within 24h. The secondary outcome measures were the induction-abortion interval, the total misoprostol dose required, and side effects of the regimen. Results There was no significant difference between the two groups with regard to the abortion rates within 12h (43.2% in group 1 vs. 48.1% in group 2; p=0.52; relative risk [RR]: 0.81; 95% confidence interval [CI]: 0.4-1.5) and 24h (92.6% in group 1 vs. 91.4% in group 2; p=0.77; RR: 1.11; 95% CI: 0.37-3.6). The induction-abortion intervals in the two groups were of similar length (885 minutes in group 1 vs. 912 minutes in group 2; p=0.72). When the total dose of misoprostol was compared between the two groups, women belonging to group 2 on average had received significantly more misoprostol than those in group 1 (1274592g [73 doses] vs. 614432g [64 doses], respectively; p=0.000). Conclusions Sublingual administration of repeated doses of 100g misoprostol for abortion induction appears to be equally effective to that of repeated doses of 200g.