Objective: To evaluate the predictors of persistent trophoblastic disease which can lead to early diagnosis and increase the response rate to treatment. So we have studied numerous factors between two groups of molar pregnancy, those who progressed to GTT and those who were treated after evacuation. Material and Methods: In this study, 227 patients with complete molar pregnancy, referred to our Gynecology Oncology center of Imam Hospital of Tehran University of Medical Science, Iran, were enrolled. Based on their progression to GTT, they were divided into two groups. Recorded information included the following: age, number of parity, fundal height, types of blood group, platelets count, prior history of infertility, existence of theca lutein cyst, and level of serum B hcg before evacuation, chemotherapy and level of serum B hcg within 1 and 2 weeks after evacuation. Two groups of patients were compared based on factors mentioned above. Results: Among the investigated items, there was a significant difference between two groups in these factors: fundal height, frequency of complete molar pregnancy, serum B hcg level, platelet count and chemotherapy with methotrexate. (P<0.001) Eventually we identified predictive factors for GTT. Conclusion: We recommend that further evaluations are needed to confirm our results. With more documents it would be considered a scoring system to determine the risk of development of GTT and try to prevent it by early chemotherapy.