Electrosurgical ablation of the endometrium is a therapeutic choice for those patients having abnormal uterine bleeding. When ablation is followed by a hysterectomy, tissue damage due to thermal effect can be seen. From a total of 350 women with endometrial ablation, 12 required subsequent hysterectomy. The histological features found in these specimens are described and related to the elapsed time between the two surgical procedures. The mean elapsed time between ablation and hysterectomy was 19 +/- 17.3 months. Scarring with formation of additional endometrial cavities was seen in five cases, and endocervical stenosis in two cases. In seven patients, endometrial regrowth was seen at hysterectomy. Necrosis, granulomatous and foreign-body giant cell reaction, eosinophilic infiltrate and pigment-containing macrophages in the myometrium were seen in the long-term post-ablation hysterectomies. Necrosis was seen in short period post-ablation hysterectomies. Six of the seven patients with endometrial regeneration had adenomyosis in the hysterectomy specimen. Endometrial ablation induces thermal effects in the endometrium and granulomatous reaction with foreign-body giant cell reaction, fibrosis and deposition of pigment within macrophages in the myometrium. Adenomyosis is a possible explanation for endometrial regeneration in cases of ablation failure.