Ultrasonography has become an indispensable diagnostic tool in Obstetrics and Gynecology. For it is characterized by no radiation hazard of the beam and non-invasiveness of the procedure, and the pelvic organs are readily depicted with the use of the distended bladder as an acoustic window. Recent improvements in gray scale ultrasound have permitted precise anatomical details as well as numerous informations of tissue consistency, and thus have improved diagnostic accuracy. 80 proven cases of gynecologic masses were analyzed retrospectively and sonographic differential diagnosis of the intra-pelvic masses based on their outline, location and internal consistency were tried. Results were as follows: 1. Accuracy of gray scale sonography in determining the existence of the intra-pelvic masses was approximately 99%. 2. Accuracy of gray scale sonography in determining the location of the intra-pelvic masses was approximately 94%. 3. Accuracy of gray scale sonography in determining the internal consistency of the intra-pelvic masses was approximately 93%. 4. Histologic diagnosis, however, by gray scale sonography was possible only in 48% of the intra-pelvic masses. A specific diagnosis could be made in uterine leiomyoma, ovarian cyst, mucinous systadenoma, dermoid cyst and H-mole. 5. As the intra-pelvic masses associated with pregnancy were 11 of 67 cases(16%), so it is imperative to begin with ultrasonography primarily in the diagnosis of the intra-pelvic masses.