To determine the value of endovaginal sonography for evaluating women with a suspected ectopic gestation, we prospectively studied a group of 84 pregnant women in whom conventional transabdominal sonograms failed to show a living embryo. Of 84 patients studied, 25 had an ectopic gestation, 32 had a normal intrauterine pregnancy, and 27 had an abnormal (nonviable) intrauterine pregnancy. Endovaginal sonography, compared with transabdominal sonography, provided additional information in 50 cases (60%) and less information in only three cases (4%). Of 25 ectopic gestations, endovaginal sonography provided new information in 15 cases (60%) including detection of an extrauterine gestational sac (10 cases), extrauterine embryo (two cases), or adnexal mass (three cases) not observed on transabdominal sonography. Of 32 normal intrauterine pregnancies, endovaginal sonography provided additional information in 26 cases (81%) including detection of a yolk sac (14 cases), living embryo (11 cases), or small gestational sac (one case) not seen on transabdominal sonography. Of 27 abnormal intrauterine pregnancies, endovaginal sonography showed additional information in nine cases (33%) including detection of embryonic demise (three cases), retained intrauterine products (four cases), or a yolk sac (two cases) not seen on transabdominal sonography. Patient acceptance of endovaginal sonography was excellent; 82% of the patients preferred this method to transabdominal sonography, 13% expressed no preference, and 5% preferred transabdominal sonography. We conclude that endovaginal sonography can provide significant additional information in the majority of women who are referred for sonography with a suspected ectopic gestation. We believe that this method should become a integral part of sonographic evaluation in women who are suspected of having an ectopic gestation when conventional transabdominal sonography fails to show a living embryo.