OBJECTIVES: Doppler ultrasonography can be used to assess neoangiogenesis, a characteristic feature of postmolar gestational trophoblastic neoplasia. However, there is limited information on whether uterine artery Doppler flow velocimetry parameters can predict gestational trophoblastic neoplasia following a complete hydatidiform mole. The purpose of this study was as follows: 1) to compare uterine blood flow before and after complete mole evacuation between women who developed postmolar gestational trophoblastic neoplasia and those who achieved spontaneous remission, 2) to assess the usefulness of uterine Doppler parameters as predictors of postmolar gestational trophoblastic neoplasia and to determine the best parameters and cutoff values for predicting postmolar gestational trophoblastic neoplasia. METHODS: This prospective cohort study included 246 patients with a complete mole who were treated at three different trophoblastic diseases centers between 2013 and 2014. The pulsatility index, resistivity index, and systolic/diastolic ratio were measured by Doppler flow velocimetry before and 4-6 weeks after molar evacuation. Statistical analysis was performed using Wilcoxon’s test, logistic regression, and ROC analysis. RESULTS: No differences in pre- and post-evacuation Doppler measurements were observed in patients who developed postmolar gestational trophoblastic neoplasia. In those with spontaneous remission, the pulsatility index and systolic/diastolic ratio were increased after evacuation. The pre- and post-evacuation pulsatility indices were significantly lower in patients with gestational trophoblastic neoplasia (odds ratio of 13.9-30.5). A pre-evacuation pulsatility index ≤1.38 (77% sensitivity and 82% specificity) and post-evacuation pulsatility index ≤1.77 (79% sensitivity and 86% specificity) were significantly predictive of gestational trophoblastic neoplasia. CONCLUSIONS: Uterine Doppler flow velocimetry measurements, particularly pre- and post-molar evacuation pulsatility indices, can be useful for predicting postmolar gestational trophoblastic neoplasia.