In order to simplify the operative technique and lower the postoperative complication rate, 354 healthy primigravidae were treated with a vaginal suppository containing 1 mg of 15-methyl-prostaglandin F2 alpha 12 hours prior to vacuum aspiration abortion in the first trimester. The mean cervical diameter found at the operation was 8.5 mm and in 38% of the women no further mechanical dilatation of the cervix was needed. The amount of bleeding during the operation was low (mean 30 ml, max. 300 ml). No perforations of the uterus or cervical lacerations occurred at operation. Side effects of the prostaglandin such as vomiting, diarrhea and lower abdominal pain occurred in 80% of the women and must be regarded as disturbing to the patient and seem to require that the women be hospitalized. The incidence of genital infection following the abortion was found to be 6.2%. In 8.2% of the women, the postoperative bleeding persisted for more than 14 days. It is concluded that if the frequency of side effects can be lowered by using new analogues of prostaglandins, pretreatment with vaginal suppositories may be recommended before vacuum-aspiration at legal abortion in the first trimester.