OBJECTIVE: To compare 2.7- and 4-nim rigid optics, with 3- and 5-mm outer sheaths, respectively, in office diagnostic hysteroscopy by evaluating pain, patient tolerability, optical view and diagnostic accuracy of the procedure. STUDY DESIGN: Three hundred seventy-one consecutive patients undergoing hysteroscopy were included in a prospective, randomized clinical trial, and the outcomes were analyzed. A saline solution was used as the distension medium. The t test for unpaired samples, X-2 tables of contingency and ANOVA 2 x 3 were used where appropriate. The study took place at Tor Vergata University Hospital of Rome, Rome, Italy. The 371 women were referred consecutively for suspected endometrial pathologies and were separated into 2 groups. Diagnostic accuracy of the hysteroscopic procedure, pain experienced by the 2 groups (as assessed by a visual analogue score) and patient acceptability were assessed with a questionnaire. RESULTS: Satisfactory hysteroscopy was achieved in 253 of 310 patients with a 2.7-mm hysteroscope and in 47 of 61 patients with a 4-mm hysteroscope. This difference was not significant. Menopausal status was the most important factor influencing the practicability of the hysteroscopic procedure (p < 0.001). CONCLUSION: The narrower-diameter hysteroscopes tended to lower the incidence of pain associated with office hysteroscopy, but this was not significant. Parity did not show any influence on hysteroscopic practicability. Menopausal status was the most important factor influencing the feasibility of the hysteroscopic procedure.