Purpose: The goal of this study was to perform a retrospective analysis of the ultrasonographic findings associated with low-grade endometrial stromal sarcoma. Methods: Ten pathologically confirmed cases of low-grade endometrial stromal sarcoma at our institution from January 2007 to April 2014 were retrospectively reviewed. All patients underwent a preoperative transvaginal ultrasound. Two radiologists came to a consensus regarding the location, size, margin, and echogenicity of the tumor, as well as the presence of intratumoral cystic degeneration and its extent and configuration. Results: Low-grade endometrial stromal sarcoma manifested as an intramural mass protruding into the endometrial cavity (n=6) or as a purely intramural mass (n=4). The maximal diameter of the lesion ranged from 4 to 9.1 cm (mean, 6.2 cm). The imaging features of low-grade endometrial stromal sarcoma were variable: six cases involved predominantly solid masses containing cystic degeneration, one was a predominantly unilocular cystic mass, two were ill-defined infiltrative solid masses, and one was a well-defined solid mass. Among the seven cases with internal cystic degeneration, five patients showed a multiseptated cystic area or a cystic area with multiple small clusters, while a unilocular cystic area within the tumor was found in two patients. Conclusion: Low-grade endometrial stromal sarcoma is associated with variable ultrasonographic findings with regard to the location, margin, and configuration of the lesion. Multiseptated cystic areas and multiple small areas of cystic degeneration are common.