35 breech presentations at 35.8 ± 3.4 weeks of pregnancy (mean ± SD) were studied by ultrasound immediately before attempting external version. The placenta was located on the anterior wall of the uterine cavity significantly more often in the patients in which external version did not succeed and no spontaneous version occurred (48.6%) than in those in which external version succeeded or spontaneous version to cephalic presentation occurred. The relation of uterine volume to fetal dimensions in the former group was significantly more often smaller than could be expected in relation to the duration of pregnancy. The successful manipulation group included significantly more cases in which the back of the fetus was directed ventrally or dorsally from the maternal midline than did the breech presentations in which version did not occur. The birth weight was also significantly greater in the former group. Our results indicate that ultrasonic examination of the position and size of the fetus, the location of the placenta and the uterine volume is recommended before undertaking an attempt at performing external version of a breech presentation. It is sensible not to attempt this procedure, if the placenta is located on the anterior wall, if the fetus is small and if there is a small ratio between uterine volume and fetal dimensions.