PURPOSE: To analyze the ultrasonographic findings of uterine leiomyosarcoma and to differentiate them from leiomyoma. MATERIALS AND METHODS: From January 1998 to December 2001, a retrospective review of ultrasonographic findings of 7 patients with pathologically proven uterine leiomyosarcoma and 30 patients with leiomyoma was done. RESULTS: The mean size of leiomyosarcoma was 72x59x74 mm while the echogenicity, mixed. The shape of masses was round in five cases and ovoid in two. The margins of the mass were well-defined in five cases and partially indistinct in two. The locations of the mass were intramural in four cases, submucosal in two cases and indetermined in one case. The masses abutted the endometrium in four cases while invasion into the endometrium was seen in three. All masses were single. On the other hand, the mean size of leiomyoma was 52x45x49 mm. The echogenicities were homogenously hypoechoic in eighteen cases and mixed in twelve. The shape of masses was round in nineteen cases and ovoid in eleven cases. The margins of the mass were well-defined in twenty nine cases and partially indistinct in one case. The locations of the mass were intramural in twenty five cases, subserosal in four cases, and indetermined in one case. Separation between the masses and endometrium was definite in twenty two cases while the masses abutted the endometrium in seven cases. The invasion of the masses into the endometrium was noted in one case. Twenty five cases showed multiple masses while the remaining five cases were single mass. CONCLUSION: The possibility of leiomyosarcoma should be taken in to consideration when there is a single uterine mass larger than 7cm that abutted the endometrium.