The results of the studies comparing the pain experienced by the patients undergoing conventional office hysteroscopy or mini-hysteroscopy were mixed. Several studies revealed that mini-hysteroscopy significantly reduced the procedure related pain and other studies revealed that the use of mini-hysteroscope was not associated with significant reduction in the procedure related pain. The aim of this study is to evaluate the effect of hysteroscope diameter on the pain experienced by nulliparous patients undergoing diagnostic office hysteroscopy.