This study aims to estimate the effect of adding office hysteroscopy to the preoperative diagnostic work-up in abnormal uterine bleeding on the diagnostic accuracy. It is a prospective comparative diagnostic trial at a tertiary care referral facility and a university hospital. There were a total of 295 patients, more than 35 years old, with abnormal uterine bleeding. The patients had vaginal sonography, office hysteroscopy, and office endometrial biopsy on onestop bases. The diagnostic accuracy of each method in diagnosing focal lesion and endometrial hyperplasia was measured as the main outcome of this paper. Combined hysteroscopy and biopsy were taken as the gold standard for diagnosing focal lesion while endometrial biopsy alone was the gold standard for diagnosing endometrial hyperplasia. Office hysteroscopy was superior to other methods for diagnosing focal lesion with about half of the focal lesions failing to be diagnosed with the other two methods. Office hysteroscopy was superior to vaginal sonography in diagnosing endometrial hyperplasia. Office hysteroscopy is an indispensable tool for diagnosing abnormal uterine bleeding and without its use, half of the focal lesions could be missed. Office setting and the one-stop approach greatly facilitate the use of the combination of office hysteroscopy with vaginal sonography and office endometrial sample.