Determination of the type of pelvic mass by pelvic sonography was improved significantly when a transvaginal study was performed after transabdominal sonography. Of 34 patients who underwent both studies, transvaginal sonography (TVS) was considered to add diagnostic information in 24 (70%); transabdominal sonography (TAS) was better than TVS in 4 (12%); TVS was equivalent to TAS in 5 (15%), and neither were accurate in 1 (3%). It is concluded that the use of transvaginal sonography as an adjunct to TAS is warranted for evaluating most pelvic masses; especially those confined to the true pelvis.