To determine the predictability of ectopic gestation by transvaginal sonography, we have prospectively studied 234 patients who were clinically suspicious of ectopic gestation. Of 234 patients, 143 had an ectopic gestation, 16 had a viable intrauterine pregnancy, 19 had a nonviable intrauterine pregnancy, 16 had an ovarian cyst, 15 had a pelvic inflammatory disease and the remaining 25 did not have nay pathologic lesion. Of 136 ectopic gestation which were corresponded to sonographic findings, transvaginal sonography provided important informations i.e. extrauterine gestational sac (61 cases). tad-pole appearance of hematosalpinx (49 cases), nonspecific adnexal mass (28 cases), tad-pole appearance of hematosalpinx (49 cases), nonspecific adnexal mass (28 cases), and hypoechoic masses(3 cases). Extrauterine gestational sac showed fetal pole with definite heart beat in 14 cases, fetal pole without heart beat in 8 cases and yolk sak without fetal pole in 15 cases. Follow-up tra svaginal sonography performed 5 das after the initial sonography provided additional information, that is, newly developed extrauterine gestational sac (7 cases), hematosalpinx (4 cases). fetal heart beat (2 cases), and the yolk (1case). Interval growth of the extrauterine gestational sac (3cases) and of the hematosal pinx 95 cases0 were noted on the follow up study. In all cases, patients accepted well with the procedure of transvaginal sonography without any complaint. The application of the transvaginal sonography as an initial screening test for the evaluation of ectopic gestation had an excellent diagnostic predictability with sensitivity 95.1%, specificity 78%, positive predictive value 87.1% and negative predictive value 91 %.