Since two mullerian defects, the septate and bicornuate uteri, are no longer repaired by means of the same operative approach, an accurate preoperative diagnosis of these anomalies is now critical. A septum can be removed by means of hysteroscopic metroplasty. However, repair of a bicornuate uterus still requires abdominal surgery. Hysterosalpingography (HSG) has been the primary diagnostic modality for mullerian defects. On the basis of 63 patients, HSG findings alone, as interpreted by the radiologist, had a diagnostic accuracy of 55%. When this was supplemented with a gynecologic evaluation, the diagnostic accuracy improved to only 62.5%. However, when a diagnostic protocol that include ultrasound (US) examination with HSG was used for evaluating mullerian defects, the diagnostic accuracy improved to 90%, with all errors being noncritical. Therefore, it is concluded that HSG alone is not adequate to make the distinction between a septate and a bicornuate uterus unless the angle of divergence of two straight uterine cavities is 75 degrees or less, indicating a septate uterus. Luteal-phase US is frequently necessary to distinguish between these anomalies or to diagnose them in combination.