Objective: To investigate the effectiveness and side effects of intravaginal misoprostol 400 micrograms compared with a placebo for facilitating complete abortion in cases of blighted ovum. Design: A prospective randomised placebo-controlled trial. Setting Rajavithi Hospital, Thailand between 1 July 1998 and 31 January 1999. Sample Fifty-four pregnant women with gestations of up to 12 weeks whose diagnosis of blighted ovum had been made by transvaginal ultrasound. Methods:  The patients were assigned randomly into two equal groups; the study group received two tablets of vaginal misoprostol (200 micrograms/tablet), and the control group received two tablets of a vaginal placebo. Results: The complete abortion rate was significantly higher in the women receiving misoprostol (63%) compared with those receiving the placebo (18.5%) (p < 0.05). Lower abdominal pain (74.1%) and fever (14.8%) were significantly higher in the study group than in the placebo group (22.2%) and (0%) respectively (p < 0.05). Conclusion: Intravaginal 400 μg misoprostol is significantly more effective for termination of blighted ovum than placebo, but lower abdominal pain and fever are signifcantly higher in the misoprostol group.