Study Objective: Several studies have been published on hysteroscopic treatment of cesarean scar defect using the 26 Fr resectoscope. This study compared the effects of the 26 Fr resectoscope with those of the 16 Fr mini-resectoscope in terms of efficacy, safety profile, and peri- and postoperative complications., Design: A prospective cohort study., Setting: Tertiary care university hospital (S. Orsola-Malpighi, Bologna, Italy)., Patients: Three hundred and nine women having symptoms and with a cesarean scar defect diagnosis were divided into 2 groups according to a temporal criterion: from March 2012 to March 2015, 155 consecutive women (control group) underwent isthmoplasty with the 26 Fr resectoscope (Karl Storz, Tuttlingen, Germany), whereas from April 2015 to March 2018, 154 consecutive women (study group) underwent isthmoplasty with the 16 Fr mini-resectoscope (Gubbini system, Tontarra Medizintechnik, Tuttlingen, Germany)., Interventions: One hundred and fifty-five women (control group) underwent isthmoplasty with the 26 Fr resectoscope, and 154 women (study group) underwent isthmoplasty with the 16 Fr mini-resectoscope. The so-called "channel-like" 360° endocervical resection technique was applied., Measurements and Main Results: The isthmoplasty time with the 2 resectoscopes, excluding cervical dilatation, was similar (p = .25), whereas the overall surgical time was shorter in the case of the mini-resectoscope. The use of the 16 Fr mini-resectoscope was significantly associated with a reduced volume of distension medium used (p <.001) and a lower fluid absorption (p <.001). A significant increase (p = .01) in postoperative complications in the control group (9/155; 5.8%) compared with the study group (1/154; 0.7%) was also found. No significant reduction in discharge time was observed between the 2 groups (p = .13). Patient satisfaction immediately after surgery was significantly higher (p <.001) in the study group than in the control group., Conclusion: Isthmoplasty with a 16 Fr mini-resectoscope seems to be as effective as isthmoplasty with a 26 Fr resectoscope in reducing postmenstrual abnormal uterine bleeding and suprapubic pelvic pain. It is associated with a significant reduction in overall surgical time owing to the non-necessity of performing cervical dilatation. The 16 Fr mini-resectoscope facilitates surgery in small anatomical spaces such as the cervical canal and reduces the complication rate linked to blind maneuvers not respecting the uterine anatomy., (Copyright © 2020 AAGL. Published by Elsevier Inc. All rights reserved.)