Ultrasonography is a safe, nonivasive examination which should be the first procedure in the workup of a patient with a definite or suspected pelvic mass. The diagnostic schemes were derived from correlating the sonographic features with histomorphology in 230 surgically proven pelvic masses. Besides separating pelvic masses into the conventional categories of cystic, complex and solid, gray-scale sonographic features of a pelvic mass can be used to subcategorized these masses into a more useful differential diagnosis. The results are as follows: 1. The most characteristic finding of uterine myoma was midly to mederately echogenic uterine enlargement (90.7%) with a lobulated uterine margin (62.8%), and often less echogenic than the normal uterine echoes. 2. The typical ultrasonographic finding of H-mole was uterine enlargment with multiple small vesicular patterns of intrauterine contents (93%) 3. The most frequent finding of cystic teratoma was cystic mass with echogenic foci (48%), but the echogenic appearance of the lesions was extremely variable. 4. The ultrasonographic findings of ectopic pregnancy were adnexal mass (complex or cystic), decidual proliferation of the uterus, enlargement of uterine size, fluid in cul-de-sac, deveiation of uterus by adnexal mass, and pseudointrauterine appearance.