To evaluate the effects of sublingual misoprostol on cervical dilatation before hysteroscopy. Prospective randomized study (Canadian Task Force classification I). University teaching center. Forty nulliparous women who received injection of leuprolide acetate 4 weeks before hysteroscopy, of whom 20 were randomized to treatment with misoprostol and 20 to placebo. Sublingual misoprostol 100 mug or placebo administered 12 hours before operative hysteroscopy. Misoprostol was associated with mild abdominal cramps in four women (20%) and vaginal bleeding in another. No side effects were reported among women in the placebo group. There was no difference in baseline diameter of the cervical opening between the misoprostol group (4.0 +/- 0.1 mm) and the control group (4.2 +/- 0.2 mm). Time to dilate cervix up to 9 mm was also not significantly different (misoprostol 48.4 +/- 9.2 sec, placebo 37.7 +/- 4.1 sec). We found no difference in degree of difficulty dilating the cervix between groups. Cervical tear occurred in one patient in the misoprostol group. Sublingual misoprostol 100 mug does not facilitate cervical dilatation before hysteroscopy. This may be related to leuprolide's hypoestrogenic effect.