Objective: To find out the probable reasons for endometrial ablation failure. Study design: This retrospective observational study was conducted in Basildon and Thurrock University Hospitals. Patients undergoing microwave endometrial ablation or radiofrequency ablation but required additional treatment (medical/surgical) after the procedure were included in the study. The patients having the procedure between 2012 to 2019 were followed up and included in the study. Patient’s baseline characteristics including age, BMI, presenting complaint, clinical and sonographic findings including uterine cavity length, and details of the ablation procedure were collected. The endometrial biopsy results, further treatment, and histology in patients who underwent hysterectomy were also noted and appropriate statistical analysis was conducted. Result: Among the 653 patients that underwent endometrial ablation (either radio-frequency/ microwave), from 2012 to 2019, 100 patients had ablation failure. All patients had undergone hysteroscopy and had a normal histopathology examination prior to undergoing ablation. The most common symptom of failure was a recurrence of heavy bleeding. 67% of patients with ablation failure opted for hysterectomy, 15% for repeat ablation, and 18% had medical management. The results showed that increased age, higher BMI, a larger uterine cavity, and the presence of fibroids and/or adenomyosis are associated with a higher risk of endometrial ablation failure. Conclusion: This study provides insight into the salient factors contributing to ablation failure which may guide future decisions toward better patient selection and counseling for endometrial ablation.