Introduction: National Institute for Health and Care Excellence Guideline 88 advocates outpatient hysteroscopy in preference to transvaginal ultrasound for premenopausal women with heavy menstrual bleeding, who are suspected of having submucosal fibroids, polyps or endometrial pathology. The guideline, however, analysed outdated studies that provided low-quality evidence. This study aimed to assess the diagnostic accuracy of transvaginal ultrasound in detecting endometrial pathology; and to evaluate the cost-effectiveness of outpatient hysteroscopy if it were to be used in preference to transvaginal ultrasound. Methods: A health service evaluation was conducted at a district general foundation trust between 1 January 2019 and 31 March 2019 of all premenopausal women with heavy menstrual bleeding. A cost-effectiveness analysis was also performed to evaluate the financial implication of outpatient hysteroscopy being used in preference to transvaginal ultrasound. Results: 100 patients were included in the study. For the detection of endometrial pathology, transvaginal ultrasound had a positive predictive value of 65.2%; negative predictive value of 98.5%; sensitivity of 93.75%; specificity of 88.89% and an accuracy of 89.77%. For identifying endometrial polyps, submucosal fibroids and endometrial thickening, transvaginal ultrasound had a positive predictive value of 33.3%, 85.7% and 50%, respectively. It would have cost the Trust 78.7% more if National Institute for Health and Care Excellence’s recommendation was carried out, with a 23.4% increase in workload in the hysteroscopy department, and a decrease of 7.8% transvaginal scans performed. Conclusion: Outpatient hysteroscopy is costly and would increase the workload burden in the hysteroscopy department. Transvaginal ultrasound has a high sensitivity, specificity and accuracy in detecting endometrial pathology therefore it should remain as the initial diagnostic investigation.