The objectives of the present clinical study were to evaluate the safety and efficacy of misoprostol (Cytotec) self-administered into the vagina for medical abortion in adolescents under the age of 18 years. After obtaining written consent from the patients and parents or guardians, a group of 150 adolescents with gestations between 35 and 63 days received 800 microg of vaginal misoprostol every 24 h, up to a maximum of three main doses, for abortion. Outcomes assessed included successful abortion (complete abortion without surgery), side-effects, decrease in hemoglobin, mean time of vaginal bleeding, mean expulsion time and mean time for the return of menses. Complete abortion occurred in 133/150 (88.7%, 95% confidence interval 82-93) patients. The frequencies of nausea, vomiting and diarrhea were statistically significantly higher when compared to those obtained for adult females. Vaginal bleeding lasted for 12.7 +/- 5.7 days (median 12 days, range 1-23 days). The mean expulsion time was 6.8 +/- 2.4 h (median 6 h, range 3-14 h) for those who aborted after the first misoprostol dose. The mean time for the return of menses, for those who aborted with misoprostol, was 34.7 +/- 3.4 days. The mean decrease in hemoglobin was statistically significant (p = 0.001), but had no clinical relevance. Taking into account the high abortion rate obtained, we could conclude that misoprostol alone is a valid method for terminating unwanted pregnancies in adolescents under the age of 18 years.