Objective: To evaluate the clinical effectiveness and safety of a thermal balloon system to ablate the endometrium. Methods: All 18 patients were candidates for hysteroscopic endometrial ablation or hysterectomy for menorrhagia and consented to a trial of the balloon technique of ablation. All procedures were done in the operating room under general anesthesia, except in one patient who had regional and another who had local anesthesia with analgesia. Follow‐up of 6‐34 months is reported. Results: Fifteen subjects (83%) reported significant reduction in bleeding or amenorrhea. Two patients underwent subsequent hysterectomy and one a follow‐up hysteroscopic examination with biopsy. Histology in these three cases showed areas of scar as well as areas of normal endometrial histology. In one uterus, the entire cavity and the endometrium were normal. The others had endometrial bands of scar and some contraction of the cavity. Conclusions: Based on follow‐up results, the frequency of successful reduction of bleeding and/or amenorrhea in this small series is comparable to hysteroscopic methods of endometrial ablation. There were no complications. A larger trial is warranted to compare this method to hysteroscopic endometrial ablation. (Obstet Gynecol 1994;83:732‐4)