Aim The aim of this study was to identify the preoperative diagnostic findings suggestive of uterine sarcoma. Methods We retrospectively reviewed the medical records of 31 patients with pathologically confirmed uterine sarcoma including leiomyosarcoma, endometrial stromal sarcoma, and undifferentiated sarcoma, between 2003 and 2011. The cases were matched by age, year of procedure (plus or minus 1 year), and surgeon, to controls (1:3 ratio) selected from all the patients who underwent hysterectomy for uterine myoma during the same period. Results Uterine sarcomas had larger tumor size compared with leiomyoma on sonography (P = 0.006). There was no significant difference in the total number of masses found on ultrasonography (P = 0.066). On multivariate analysis increased neutrophil‐to‐lymphocyte ratio (NLR > 2.1), large tumor size (> 8.0 cm), and lower body mass index (BMI ≤ 20) were independent risk factors for uterine sarcoma (P = 0.014, 0.048, and 0.048, respectively). Sarcoma index was calculated by summing the number of risk factors. Higher sarcoma index was associated with increased risk of uterine sarcoma (0, 13.6%; 1, 21.7%; 2, 62.5%; 3, 100%). Conclusion Preoperative NLR, tumor size, and BMI could be useful for the discrimination of sarcoma from leiomyoma of uterus.