The authors retrospectively reviewed 45 consecutive cases of proven ectopic pregnancy for which both transvaginal (TV) and transabdominal (TA) ultrasonography had been performed to compare the diagnostic efficacy of the two imaging techniques. The criteria for a diagnosis of ectopic gestation included an extrauterine gestational sac containing a fetus or a fetal pole, or an empty extrauterine sac. Solid or complex adnexal masses with evidence of hemoperitoneum were considered suggestive but nondiagnostic. TV ultrasonography was superior to TA ultrasonography in 22 cases (49%) and inferior in 3 (7%). In the remaining 20 cases (44%) the two methods yielded similar information. For cases in which TV ultrasonography was superior, this method provided clear evidence of ectopic pregnancy in 11 cases in which TA ultrasonography demonstrated nonspecific masses or normal adnexa; in the other 11 cases both methods led to the correct diagnosis, but TV ultrasonography provided additional useful information. The authors conclude that TV ultrasonography has a definite role in improving the diagnosis of ectopic pregnancy.