To investigate whether telomerase is activated in complete hydatidiform mole and whether it could predict the development of persistent gestational trophoblastic tumors (GTTs).For this prospective study, 21 patients with complete hydatidiform mole were recruited. Molar tissue was obtained for telomerase activity measurement using the telomeric repeat amplification protocol assay. Patients' clinical characteristics, telomerase activity and subsequent clinical outcome were analyzed.Telomerase activity was detected in 12 cases (57.1%) with varied intensity. Two of four patients who had telomerase activity, uterine size larger than expected and preevacuation serum beta-human chorionic gonadotropin (beta-hCG) levels > 10(6) mIU/mL developed persistent GTT.Telomerase activity is detectable in some complete hydatidiform moles and might be useful for predicting persistent GTT when combined with uterine size and preevacuation serum beta-hCG level.