While nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to improve survival in certain cancers, data in patients with endometrial cancer (EC) is conflicting. This study investigated use of aspirin and nonaspirin NSAIDs (NA-NSAIDs) and EC-specific-and all-cause death. This nationwide cohort study linked data from the Cancer Registry of Norway with The Norwegian Prescription database. Patients diagnosed with EC from 2004 to 2018 were included. Post-diagnosis exposure to aspirin and NA-NSAIDs was defined as ≥3 consecutive prescriptions ≥30 days after EC diagnosis, with pre-diagnosis use as ≥2 filled prescriptions <
6 months prior to diagnosis. Follow-up started 10 months after diagnosis. Hazard ratios for the risk of death were calculated with multivariable Cox-regression models. Our study population included 7751 individuals with EC, 685 (9%) were aspirin users and 620 (8%) were NA-NSAIDs users. The median follow-up time was 5.0 years, with 1518 (20%) deaths observed (n = 728 (9%) EC-specific). In multivariable analysis, aspirin use was significantly associated with a 19% higher risk of all-cause death compared to non-users (HR = 1.19, 95% CI [1.01-1.41]). The association was stronger among combined pre- and postdiagnosis use (HR = 1.35 [1.12-1.64]). NA-NSAIDs use increased risk of cancer-related death (HR = 1.25 [0.99-1.58]) and there was a dose-response association with significantly higher risk of cancer-specific death with higher cumulative doses (HR = 1.33 [1.02-1.75]). We found a higher risk of cancer-specific-and all-cause death among patients that used aspirin and NA-NSAIDs after a diagnosis of EC. Further studies on the biological mechanisms underlying these associations are needed.