Background: Recent data suggest that the use of nonsteroidal anti-inflammatory drugs (NSAIDs) may be associated with reductions in endometrial cancer risk, yet very few have examined whether their use is related to prognosis among endometrial cancer patients. Methods: Study subjects comprised 4374 participants of the NRG Oncology/Gynecology Oncology Group 210 Study with endometrial carcinoma who completed a presurgical questionnaire that assessed history of regular prediagnostic NSAID use and endometrial cancer risk factors. Recurrences, vital status, and causes of death were obtained frommedical records and cancer registries. Fine-Gray semiproportional hazards regression estimated adjusted subhazard ratios (HRs) and 95% confidence intervals (CIs) for associations of NSAID use with endometrial carcinoma-specific mortality and recurrence. Models were stratified by endometrial carcinoma type (ie, type I [endometrioid] vs type II [serous, clear cell, or carcinosarcoma]) and histology. Results: Five hundred fifty endometrial carcinoma-specific deaths and 737 recurrences occurred during a median of five years of follow-up. NSAID use was associated with 66% (HR=1.66, 95% CI=1.21 to 2.30) increased endometrial carcinoma-specific mortality among women with type I cancers. Associations were statistically significant for former and current users, and strongest among former users who used NSAIDs for 10 years or longer (HR=2.23, 95% CI=1.19 to 4.18, two-sided Ptrend = .01). NSAID use was not associated with recurrence or endometrial carcinoma-specific mortality among women with type II tumors. Conclusions: In this study, use of NSAIDs was associated with increased endometrial carcinoma-specific mortality, especially in patients with type I tumors. Barring a clear biologic mechanism by which NSAIDs would increase the risk of cause-specific mortality, cautious interpretation is warranted.