Purpose: This study developed and validated algorithms to identify incidence of endometrial cancer using ICD-9-CM and ICD-10-CM coding systems as part of a post-authorization safety study (EU PAS: EUPAS45602) of vaginal estrogen, estrogen and progestin combination hormone therapy (EPHT), and non-users of vaginal estrogen. Methods: Using national claims data in the HealthCare Integrated Research Database (HIRD), provisional endometrial cancer cases were identified using a screening algorithm comprising at least one endometrial cancer diagnosis code at any location and position between 1/1/2007, and 12/31/2021. One medical record per case was obtained for 700 provisional cases. Two experts in obstetrics and gynecology adjudicated the medical records classifying each patient as a confirmed case, confirmed non-case, or unknown. Positive predictive value (PPV), sensitivity, and their respective 95% confidence intervals (CI) were calculated. Algorithms were generated by choosing the codes and number of encounters to balance endometrial cancer detection and false positives. Algorithms were trained in a sample of non-users of vaginal estrogen and tested across treatment groups. Results: Among non-users, two visits with ICD-9-CM code 182.0 or 182.8 had a PPV of 91.2% (85.4%-95.2%) and sensitivity of 99.3% (95.9%-100.0%). Two visits with ICD-10-CM code C54.1, C54.8, or C54.9 had a PPV of 97.0% (93.6%-98.9%) and sensitivity of 99.5% (97.2%-100.0%). PPVs and sensitivities were over 75% across cohorts for both algorithms. Conclusion: Two visits with an endometrial cancer diagnosis code accurately identified endometrial cancer cases in both coding systems. Endometrial cancer diagnosis codes were highly specific. PPVs and sensitivities were similar in all cohorts.