Purpose: This study aimed to determine the occurrence rate of gestational trophoblastic neoplasia (GTN) and its related factors in aged women with hydatidiform mole (HM) in Tu Du Hospital, Vietnam. Materials and Methods: This retrospective cohort study included 372 women aged ≥40 years with HM diagnosed through postabortion histopathological assessment in Tu Du Hospital from January 2016 to March 2019. Survival analysis was used for GTN cumulative rate estimation, log-rank test for group comparison, and Cox regression model for determining GTN-related factors. Results: After a 2-year follow-up, 123 patients were found to have GTN at a rate of 33.06% [95% confidence interval (CI): 28.30– 38.10]. GTN occurrence meant that the time was 4.15±2.93 weeks with peaks at week 2 and 3 after curettage abortion. The GTN rate was remarkably higher in the ≥46-year age group than in the 40-to-45-year age group [hazard ratio (HR)=1.63; 95%CI: 1.09– 2.44], as was the vaginal bleeding group compared to the non-bleeding group (HR=1.85; 95%CI: 1.16–2.96). Preventive hysterectomy and preventive chemotherapy plus hysterectomy in the intervention group reduced the GTN risk compared to the no intervention group at HRs of 0.16 (95%CI: 0.09–0.30) and 0.09 (95%CI: 0.04–0.21), respectively. Chemoprophylaxis failed to decrease the GTN risk when comparing the two groups. Conclusion Post-molar pregnancy GTN rate in aged patients was 33.06%, much higher than that of the general population. Preventive hysterectomy or chemoprophylaxis plus hysterectomy are effective treatment methods to support GTN risk reduction.