Preoperative differential diagnoses between uterine sarcomas and leiomyomas are difficult. As telomerase activation is thought to be essential for the immortality of malignant cells, it is considered a potentially useful diagnostic marker. The aim of the present study was to evaluate the potential diagnostic use of measuring telomerase activity in needle biopsy samples to distinguish uterine sarcoma from leiomyoma. Sixty-two patients with suspected uterine sarcomas based on clinical findings or magnetic resonance imaging findings, and who were scheduled for surgery, underwent transcervical ultrasound-guided needle biopsy. Three samples were obtained per patient for histopathological examination and telomerase activity measurement. Telomerase activity was measured using the telomeric repeat amplification protocol and correlated with final histopathological findings of surgical specimens. Of the 62 patients, 6 leiomyosarcomas and 1 endometrial stromal sarcoma (high grade) were diagnosed by histopathology. In 6 of the 7 samples from uterine sarcomas, relatively high telomerase activity (22-102 units) was detected, whereas only low telomerase activity (11-18 units) existed in 3 of the remaining 55 samples from benign or borderline uterine smooth muscle tumors. At a cut-off value of 20 units, sensitivity, specificity, positive predictive, and negative predictive values for detecting uterine sarcoma were 86% (95% confidence interval, 59-100%), 100% (94-100%), 100% (54-100%) and 98% (95-100%), respectively. The results indicated that telomerase activity in needle biopsy samples is a useful diagnostic marker to distinguish uterine sarcoma from leiomyoma.