Objective To explore the role of CT scan for the diagnosis of lung metastasis in stage Ⅲ gestational trophoblastic neoplasia (GTN).Methods To figure out the role of CT scan for lung metastasis in GTN initial diagnosis,treatment and follow-up,93 GTN patients with lung metastasis from January,2015 to December,2016 were retrospectively analyzed in Obstetrics and Gynecology Hospital of Fudan University.Results (1) Among 93 GTN patients with lung metastasis,70 patients with the International Federation of Gynecology and Obstetrics (FIGO) score ≤6 were defined as low risk GTN and 23 patients score score ≥7 were defined as high risk GTN.Forty nine patients had negative chest X-ray findings and 39 cases with pulmonary lesions were identified both by chest X-ray compared to CT scan.Five cases were excluded due to no consensus could make for the results of chest X-ray.The true positive rate of chest X-ray for lung metastasis were 41％ (29/70) in low risk GTN and 43％ (10/23) in high risk GTN patients without statistical difference (x2=0.090,P=0.925).For those patients with positive chest CT scan and negative chest X-ray finding,pulmonary lesions in 32 (65％,32/49) cases were blocked by heart,chest wall or diaphragm in chest X-ray.Seventeen (35％,17/49) patients with lung lesions less than 5 mm had negative chest X-ray results due to the lower sensitivity compared to CT scan.(2) In 88 patients with stage Ⅲ,78 patients had successful initial treatment,but 4 of them were recurrence in twelve months follow-up.Ten patients were chemotherapy resistance for the initial treatment.The initial chemotherapy remission rate in low risk GTN patients was higher than that in high risk ones (x2=4.911,P=0.027).In 49 cases with negative chest X-ray,there was no correlation with the rate of remission,chemotherapy resistance and recurrence in stage Ⅲ patients (P＞0.05).(3) For those patients who had poorly response to initial chemotherapy,the diameters of lesions in lung were unchanged or increased during the treatment,form (5.1±4.1) mm to (7.4±2.8) mm.The pulmonary lesions were continuously shrunk from (7.8 ± 5.3) mm to (4.7 ± 4.4) mm for those patients with complete and partial remission including the recurrent GTN patients (Z=-2.713,P=0.007).Conclusions Patients with GTN in stage Ⅲ have down staging if only use chest X-ray for imaging at the initial diagnosis.Chest CT scan is recommended for primary imaging evaluation of FIGO staging in qualified medical organization.For those patients with persistent abnormal serum hCG level and negative chest X-ray,chest CT scan is strongly recommended to identify the persist or resistant lung lesions and follow up.